Assalamualaikum, how do we know the person with Musa (peace be upon him) was Khidr (peace be upon him)? As the name is not mentioned din Quran..
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
The story of Al-Khidhr and Moosa (Moses), may Allaah exalt their mention, was already mentioned in the Quran without mentioning the name of Al-Khidhr. Allaah Says (what means): {And they found a servant from among Our servants [i.e. al-Khidhr] to whom We had given mercy from Us and had taught him from Us a [certain] knowledge.} [Quran 18:65]
However, the Sunnah clarified that his name was Al-Khidhr. In Saheeh Al-Bukhari, the Prophet said about the story of Al-Khidhr and Moosa that when Moosa claimed to be the most knowledgeable man on earth: ''Allaah revealed to Moosa: Of course, there is our servant Al-Khidhr (who has better knowledge than you)….”
Besides, Al-Bukhari reported in his Saheeh that the Prophet said: ''He was named Al-Khidhr (which literally mean the green man) because he sat on a barren land and the ground turned green with vegetation behind him.”
For more benefit, please refer to Fatwa 82168.
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