Abdullah bin Umar (r.a.)
There is no doubt that all of the Companions made great efforts to value the Sunnah and to be subject to it. However, some of them were more adherent and devoted to the Sunnah than others. One of them was so adherent to it that he worked meticulously to follow the Messenger of Allah exactly. He imitated the Prophet in not only matters concerning worshipping but also human affairs. For example, when he went somewhere that the Messenger of Allah went, he would follow the same route, stop in the same places, made wudu and performed prayers in the same place as the Messenger of Allah did. The Muslims knew this and they did whatever he did as sunnah without hesitation.
Once, he had all of his hair cut. While he was having his hair cut, he said to the people around, "O people! It is not sunnah. I am having my hair cut because it gives me pain." For, he was worried that people would do so thinking that it was sunnah. This Companion was Abdullah, Hz. Umar's son.
Hz. Abdullah was a child aged about five years old when his father became a Muslim. Therefore, he never worshipped idols. When he became old enough to understand Islam, he became a Muslim at once. Then he migrated to Madinah.
When Abdullah became a youth, he wanted to join the army prepared for the Battle of Badr but the Prophet did not allow him and a few more youths to join the army. This distressed Abdullah a lot. He stated the following regarding the issue:
"He did not allow me to join the war because he found me small. I do not remember any other night when I did not sleep a wink until the morning, and tossed and turned by weeping. "
Hz. Abdullah could not join the Battle of Uhud because he was too young. However, after this battle, he joined all of the wars with the Prophet. The Messenger of Allah appreciated him due to his great heroism. 
Abdullah joined Ashab as-Suffa, who devoted themselves to learning Islam only and who were not engaged in any other work, after the Migration. He started to sleep in the mosque with them. Thus, beginning from a very young age, he learned from both the Prophet and the Companions he stayed with. He increased his knowledge. He soon became one of the distinguished people of Ashab as-Suffa. He participated in the circles of learning (ilm). He acquired deep knowledge related to Islamic affairs.
The Prophet loved Abdullah a lot; he gave Abdullah some advice from time to time. Once, he held Abdullah, who was still very young at that time, on the shoulder and said, to him,
“O Abdullah! Accept yourself as a lonely passenger in the world and as a person in the grave. O son of Umar! There is neither dinar nor dirham in the hereafter; goodness and evil are compared there. Allah will not look at the faces of those who drag their clothes with prides.” 
After that, Hz. Abdullah lived in accordance with this advice throughout his life.
When Hz. Abdullah was sleeping in the mosque, he saw a dream. Two angels took him to Hell. He started to say, “I take refuge in Allah from Hell. I take refuge in Allah from Hell. I take refuge in Allah from Hell.” Meanwhile, another angel joined them. He said to Abdullah, “Do not fear!” Abdullah narrated this dream to Hafsa, his sister and asked her to ask the Prophet about it. The Messenger of Allah said, “Abdullah is a very good man. If only he would perform prayers at night.” After that, Abdullah slept very little at night. He performed tahajjud prayer at night. 
Abdullah loved the Messenger of Allah a lot. His heart, his soul, his whole being was filled with his love. Due to this love, he never left the Messenger of Allah for a moment except for his necessary affairs. He learned a lot from the school of the prophethood. The Prophet died like all of the ephemeral beings. This separation distressed Hz. Abdullah a lot. Whenever the Messenger of Allah was mentioned, he could not help shedding tears. Whenever he set out on a journey and returned from a journey, he would first visit the tomb of the Prophet.
During the caliphate of Hz. Umar, his father, Abdullah took part in the conquest of Egypt, North Africa, Khorasan and Tabaristan. He helped his father in administrative issues. He settled the complicated issues that Muslims confronted. The most obvious characteristic of Abdullah, who was one of the Companions (stars) that would guide the Muslim generations up to the Day of Judgment, in following the Sunnah was his generosity. This lucky Companion acted in accordance with the following verse: “By no means shall ye attain righteousness unless ye give (freely) of that which ye love.” His exemplary attitudes are given as examples in the narrations about it.
Once, he got on his camel. He liked the way his camel walked.
He said, "How nice! How nice!" Then, he made the camel stop and sit. He told Hz. Nafi, who was with him, to remove the saddle from the camel. When the saddle was removed, he said to Nafi,
"Have you ever seen a camel with such a beautiful head?" Now, it was clear that he would sacrifice this beautiful camel in hajj. Nafi said to him,
"It would be a pity. If you sold this camel, you could buy a few camels to sacrifice with the money." However, Abdullah ignored what he said and told him to mark the camel and put it among the camels to be sacrificed. For, it was basic principle in his life to sacrifice the things that he liked most in the way of Allah. 
Abdullah bin Umar's most famous characteristic is his taking care of the poor, the orphans, and the people without any friends or relatives. Hz. Abdullah always made sure that there was an orphan or a poor person at the table when he had a meal. When he sat at the table for lunch and dinner, he immediately informed the orphans living around and started eating after they arrived. When he walked out of the mosque, he would take the poor he met on the way to his house and feed them. His wife often felt sorry for him because he would often go hungry due to this custom because Hz. Abdullah gave all his food to the poor. Therefore, once, his wife informed the poor waiting at the exit of the mosque that she would give them food. When Hz. Abdullah came out of the mosque, he could not find anyone on the way. When he got home, he said,
"Call me such and such people." His wife, said, “I sent food to them.” He said, “Your aim is probably not to make me eat a meal.” He did not eat lunch and dinner that day. 
An exemplary anecdote for us from his exemplary and harmonious life is mentioned in the book called “Lem’alar”.
One day while shopping in the market, in order to be economical and to preserve the confidence and integrity on which trade depends, Hz. Abdullah disputed hotly over something worth a few kurush. One of the Companions saw him, and imagining the Illustrious Successor of the Prophet on Earth, the Caliph ‘Umar’s son’s wrangling over a few kurush to be an extraordinary stinginess, he followed him in order to understand his conduct.
Next, he saw that ‘Abdullah was entering his blessed house and had spotted a poor man at the door. He chatted with him for a bit, and the man left. Then he came out of the second door of the house and saw another poor man. He chatted with him for a while too, and the man left. The Companion, who was watching from the distance, was curious. He went and asked the poor men: “‘Abdullah paused a while with you. What did he do?” Each of them replied: “He gave me a gold piece.” “Glory be to Allah!,” exclaimed the Companion, and thought to himself: “How is it that he wrangled like that over a few kurush in the market, then was completely happy to give away two hundred kurush in his house without letting anyone know?” He went to ‘Abdullah ibn ‘Umar and said: “O Imam! Solve this difficulty for me! In the market you did that, while in your house you did this.” ‘Abdullah replied to him saying:
“What I did in the market was not stinginess, but arose from frugality; it was perfectly reasonable, and to preserve confidence and honesty, which are the basis and spirit of commerce. And what I did by my house arose from the heart’s compassion and the spirit’s perfection. Neither was the first stinginess, nor the second immoderateness.”
Abdullah, whose compassion, mercy, balance and reasoning are clearly seen in the examples we have given, had a heartfelt and brave character that could utter the truth aloud in the face of oppression without hesitation. His harsh reaction against Hajjaj in the last years of his life indicates this.
On one occasion when Hajjaj, the Oppressor, lengthened the sermon of Friday too much, he shouted from the place where he was sitting,
"The sun will not wait for you!" Hajjaj said,
"I would like to cut your head!" Abdullah said,
"I know you would because you are a debauched person."
Hz. Abdullah would not accept to be an administrator because he was afraid of its responsibilities. He refused the offer Hz. Uthman made insistently each time.
Abdullah bin Umar, who was one of the “Four Abdullahs” famous in the history of ilm, had a distinguished place in tafsir, fiqh and especially hadith. He narrated 2 thousand and 630 hadiths, becoming the second person who narrated the most hadiths after Abu Hurayra.
While Abdullah narrated hadiths, he scrutinized them carefully. He would pay attention to words and even letters in the hadiths he narrated. Even if the meaning was the same, he would not use a word that was not used by the Messenger of Allah. He pronounced the words very clearly when he narrated hadiths. His listeners admired him. Some of the hadiths he narrated are as follows:
“A Muslim is a brother of another Muslim, so he should not oppress him, nor should he hand him over to an oppressor. Whoever fulfilled the needs of his brother, Allah will fulfill his needs; whoever brought his (Muslim) brother out of a discomfort, Allah will bring him out of the discomforts of the Day of Resurrection, and whoever screened a Muslim, Allah will screen him on the Day of Resurrection.” 
“Whoever has the following four characteristics will be a pure hypocrite. Whoever has one of the following four characteristics will have one characteristic of hypocrisy unless and until he gives it up. Whenever he is entrusted, he betrays. Whenever he speaks, he tells a lie. Whenever he makes a promise, he breaks it. Whenever he makes a contract, he gives it up. When he becomes an enemy, he exceeds the limits and commits evil deeds more…”
Once, the Prophet saw somebody blaming a person due to his modesty. He said,
“This modesty will harm you.” Thereupon, the Messenger of Allah (pbuh) said,
“Leave him. Modesty is part of belief.” 
Although Hz. Abdullah had a very good command of hadith, tafsir and fiqh, he acted meticulously when he issued fatwas. He would act modestly and say, "I do not know this issue" if he did not know something very well or if he hesitated. Many people were amazed by his sincere admission. Once, they wanted a fatwa from Abdullah. He said, "I do not know this issue." When the person asking about the issue insisted, Hz. Abdullah said, "I cannot build a bridge to Hell because of you."
Hz. Abdullah passed away in 73 H when he was 86 years old. The following word of his is indeed a guide to those who are in the way of knowledge (ilm):
“A person cannot be a real scholar unless he has the following qualities: He should not be jealous of anyone superior to him. He should not look down on anybody below him. He should not seek a worldly interest for his ilm.”
Usdul-Ghaba, 3: 277.
Bukhari, Riqaq: 3.
Muslim, Fadailus-Sahaba: 140.
Aal-i Imran, 192.
Usdul-Ghaba, 3: 229.
Hilya, 1: 298.
Lem’alar, p. 134.
Bukhari, Mazalim: 3; Muslim, Birr: 58.
Bukhari, Iman: 24; Muslim, Iman: 106.
Muslim, Iman: 59.