Chapter 32: Dialects and Readings of the Qur'an (Kitab Al-Huruf Wa Al-Qira'at)
Narrated Abu Sa' id al-Khudri: The Messenger of Allah (ﷺ) related a tradition in which he mentioned the words "Jibril and Mikal" and he pronounced them "Jibra' ila wa Mika' ila."Abu Dawud said: Khalaf said: I did not put the pen aside from writing letters (huruf) for forty years: nothing tired me (or made me incapable of writing), even Jibril and Mika' il did not tire me.
Sunan Abi Dawud 3998