Is it true that the Prophet Musa (Moses) killed a man? If so, is it not a big sin?

Dear Brother / Sister,

While trying to break up a fight between two men, the Prophet Musa accidentally killed one of them.He asked Allah’s for his forgiveness and Allah forgave him.

The verses are as follows:

"And he entered the City at a time when its people were not watching: and he found there two men fighting― one of his own people, and the other, of his foes. Now the man of his own people appealed to him against his foe, and Moses struck him with his fist and made an end of him. He said: "This is a work of Evil (Satan): for he is an enemy that manifestly misleads!"

He prayed: "O my Lord! I have indeed wronged my soul! Do Thou then forgive me!" So (Allah) forgave him: for He is the Oft-Forgiving, Most Merciful." (al-Qasas,28/15-16)

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