1242
Musnad AhmedIt was narrated that "Asim bin Damrah said:
We came to "Ali bin Abi Talib (رضي الله عنه) and said: O Ameer al-Mu"mineen, why don"t you tell us about the voluntary prayer of the Messenger of Allah (ﷺ)? He said: Who among you can do that? They said: We will take what we can do. He said: The Messenger of Allah (ﷺ) used to pray sixteen rak"ahs during the day apart from the Prescribed prayers.
Reference: Musnad Ahmad 1242
Arabic/English book : Book 5, Hadith 1242
Arabic/English book : Book 5, Hadith 1242