Sahih Muslim 2533
صحيح مسلم#2533SahihAdi b. Hatim (Allah be pleased with him) reported that when (this verse) was revealed:" Until the white streak of the dawn becomes distinct from the dark streak" (ii. 187) Adi b. Hatim said: Messenger of Allah, verily I keep underneath my pillow two strings, one white and the other black, by which I distinguish night from dawn. Upon this the Messenger of Allah (ﷺ) said: Your pillow seems to be very large. For the word khait implies the blackness of the night and the whiteness of the dawn
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih Muslim is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 13:39