All of the heavenly books except the Quran were sent down as a whole at one time. (see Razi, the interpretation of verse 32 of the chapter of al-Furqan)
The whole Torah was sent to Hz. Musa (Moses) as a whole at one time, written on tablets.
The Psalms was sent down to Hz. Dawud (David) as a whole at one time.
The Gospel was sent down at one time but it was not written as a book when Hz. Isa (Jesus) was alive. For, the short time period of Hz. Isa's conveying the message and the conditions of the age when he lived were not suitable for it.
The Gospel that was written first was written after Hz. Isa in 70’s. Therefore, the truths conveyed by Hz. Isa could not be written instantly; the words of people were included in the Gospels that were written afterwards, causing the origin of the book to be distorted.
In the Quran, the way revelation is sent to prophets is expressed as follows:
"(O Muhammad!) Thus doth (He) send Inspiration to thee as (He did) to those before thee― Allah, Exalted in Power, full of Wisdom." (ash-Shura, 42/3)
The meaning of the verse is as follows: "He sends you and sent the prophets before you revelation like this or in the sense that will be explained later." The writer of Kashshaf states the following regarding the issue:
"That is, the meanings covered by this chapter are such meanings that Allah revealed the same, and in other chapters and to the previous prophets. Thus, Allah repeated these meanings in the Quran and all of the heavenly books. For, there is an eloquent warning and a great grace to His slaves in them."
The reason why the verb "reveals" is used in present tense not the verb "revealed"in past tense shows that it is His custom to do like that. The following also exists here: Allah's revelation to you and the prophets before you is like this revelation, which is stated and described in this chapter. For, the types of revelation are stated as follows: at the end of this chapter:
"It is not fitting for a man that Allah should speak to him except by inspiration, or from behind a veil, or by the sending of a Messenger to reveal, with Allah's permission, what Allah wills..." (ash-Shura, 42/51)
They probably symbolize these three types.
"We have sent thee inspiration as We sent it to Noah and the Messengers after him; We sent inspiration to Abraham, Ismail, Isaac, Jacob, and the Tribes to Jesus, Job, Jonah, Aaron, and Solomon, and to David, We gave the Psalms." (an-Nisa, 4/163)
The verse above shows that revelation is sent to all prophets and that there can be a similarity in the ways of revelation.(see Elmalılı, the interpretation of the relevant verses)
We learn detailed information about the ways of revelation from the hadiths of the Prophet (pbuh) and the witnessing of the Companions. The same ways are possible for Hz. Isa and other prophets.
The following classification can be made about the ways of revelation (wahy):
1. The first type of revelation is the true dreams seen by the Messenger of Allah (pbuh). These dreams are called "true dreams" (ru’ya as-sadiqa). These dreams, which the Prophet (pbuh) saw, came true later. Hz. Aisha sheds light on these dreams by saying, "There was no dream of the Prophet that did not come true like the brightness of the morning."
2. The angel of revelation puts the revelation in the heart of the Messenger of Allah (pbuh) while he is awake. This form of revelation is stated in the following hadith:
"The Holy Spirit blew into my heart this: 'No soul will die without using up his sustenance.' Therefore, fear Allah and seek your sustenance through legitimate ways." (Mundhiri, at-Targhib wat-Tarhib, 4/12)
The Holy Spirit is Hz. Jibril. There is no evidence that Jibril was visible. It is understood from the hadith that the angel conveyed the revelation without being seen.
3. Jibril conveyed revelation being disguised as a young man or a man. Many Companions report that Jibril conveyed revelation like this by seeming like Dihya, one of the Companions. This is the easiest and least troubled way of revelation.
4. The angel brings revelation to the Prophet (pbuh) without being seen. The Prophet heard a clanging like a gong or bell. This is the hardest form of revelation. This form of revelation is related to the verses involving threats and warnings. The Messenger of Allah (pbuh) describes this kind of revelation as follows:
"Revelation sometimes came with a sound like the clanging of a gong or bell. This one is the hardest one for me." (Bukhari, Bad’ul-Wahy, 1/2; Muslim, Fadail, 87)
During the time when such revelation came, the Prophet (pbuh) would shake, sweat and feel disturbed. It is stated in a hadith reported from Ibn Abbas that the Messenger of Allah had difficulty in memorizing the verses and that he moved his lips. Allah Almighty warned His Prophet as follows: in a verse:
"Move not thy tongue concerning the (Qur'an) to make haste therewith. It is for Us to collect it and to promulgate it: But when We have promulgated it, follow thou its recital (as promulgated)." (al-Qiyama, 75/16-18)
After the revelation of this verse, the Messenger of Allah (pbuh) would listen to Hz. Jibril and read the verses like him after he left.
5. The angel appears in his original form, brings the order of Allah to the Prophet (pbuh) and reads it. Hz. Jibril brought revelation like this twice. The first one was at the beginning of the prophethood. The Prophet (pbuh) fainted then. The second one took place during Miraj (Ascension). The following verse can be mentioned as evidence:
"For indeed he saw him at a second descent. Near the Lote-tree beyond which none may pass." (an-Najm, 53/13,14)
6. The Messenger of Allah (pbuh) speaks to Allah when he is awake. There is no intermediary in such talk. The prayers being rendered fard took place like that. The following verse can be mentioned related to this way of revelation:
"And to Moses Allah spoke direct." (an-Nisa, 4/164)
7. Hz. Jibril brings revelation to the Prophet (pbuh) while he is asleep. It is reported that the chapter of al-Kawthar was sent down like that.