When the verse was revealed, "until the white thread of dawn becomes distinct to you from the black thread" [Baqarah 2:187], I took a black cord and a white cord and placed them under my pillow. I kept looking at them during the night, but I could not tell them apart. So I went to the Messenger of Allah ﷺ in the morning and mentioned this to him.He said, "That refers only to the darkness of the night and the brightness of the day."In another narration, the man said, "I place under my pillow two cords, one white and one black, so that I may distinguish the night from the day."The Messenger of Allah ﷺ replied, "Your pillow must be very wide indeed! It refers only to the darkness of the night and the brightness of the day."
لما نزلت: {حتى يتبين لكم الخيط الأبيض من الخيط الأسود من الفجر} [سورة البقرة: ١٨٧] عمدت إلى عقال أسود وإلى عقال أبيض، فجعلتها تحت وسادتي، فجعلت أنظر في الليل فلا يستبين لي، فغدوت على رسول الله ﷺ فذكرت له ذلك فقال: إنما ذلك سواد الليل وبياض النهار. وفي رواية: إني أجعل تحت وسادتي عقالين، عقالا أبيض وعقالا أسود أعرف الليل من النهار. فقال رسول الله ﷺ: إن وسادتك لعريض! إنما هو سواد الليل وبياض النهار.
Bukhari narrated it in the Book of Fasting (1916), and Muslim in the Book of Fasting (1090), both from the hadith of Husayn bin Abdul-Rahman, from Shaybi, from Adi bin Hatim, who mentioned it. The second version is Muslim's. In a version by Abu Dawud (2349), it reads, "The Messenger of Allah ﷺ laughed and said, 'Your pillow was...'"