The Messenger of Allah (ﷺ) said: Eat and drink; let not the white and ascending light prevent you from (eating and drinking); so eat and drink until the red light spreads horizontally.
Sunan Abi Dawud Book 14, Hadith 36
← Previous Hadith The Messenger of Allah (ﷺ) as saying: The summons (adhan) of Bilal should not restrain one of you from taking a meal shortly before dawn, for he utters adhan or calls (for prayer) so that the man at prayer may return, and the man asleep may get up. Dawn is not (the whiteness) which indicates thus (in perpendicular) - the narrator Musaddad said: Yahya joined his palms (indicating the spread of whiteness vertically - until it indicates thus - and Yahya spread out two ring-fingers of his (demonstrating the spread of whiteness horizontally)l

Sunan Abi Dawud Book 14, Hadith 35 Next Hadith → When the verse "Until the white thread of dawn appear to you distinct from its black thread" was revealed, I took a white rope and a black rope, and placed them beneath my pillow ; and then I looked at them, byt they were not clear to me. So I mentioned it to the Messenger of Allah (ﷺ). He laughed and said: Your pillow is so broad and lengthy ; that is (i.e. means) night and day. The version of the narrator 'Uthman has: That is the blackness of night and whiteness of day.

Sunan Abi Dawud Book 14, Hadith 37