Sahih al-Bukhari 4509
صحيح البخاري#4509SahihNarrated Ash-Shu`bi:`Adi took a white rope (or thread) and a black one, and when some part of the night had passed, he looked at them but he could not distinguish one from the other. The next morning he said, "O Allah's Apostle! I put (a white thread and a black thread) underneath my pillow." The Prophet (ﷺ) said, "Then your pillow is too wide if the white thread (of dawn) and the black thread (of the night) are underneath your pillow
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 65:36