Adi bin Hatim reported,

When the verse was revealed, "until the white thread becomes distinct to you from the black thread of dawn" [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."

Azami 11963

Sahih

عن عدي بن حاتم قال

لما نزلت: {حق يتبين لكم الخيط الأبيض من الخيط الأسود من الفجر} 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.

الأعظمي 11963صحيح
Contents
Reference
Commentary
Ayat
Collection
Jami al-Kamil
Book
Tafsir of the great Quran
Chapter
Virtues of Surah Baqarah
Section
His saying, "It has been made permissible for you the night preceding fasting to go to your wives. They are clothing for you and you are clothing for them. Allah knows that you used to deceive yourselves, so He turned to you in forgiveness and pardoned you. So now have relations with them and seek that which Allah has decreed for you. And eat and drink until the white thread of dawn becomes distinct to you from the black thread of Fajr. Then complete the fast until the night. And do not have relations with them as long as you are staying for worship in the mosques. These are the limits of Allah, so do not approach them. Thus does Allah make clear His verses to the people."
Numbering
Jami al-Kamil 11963 (2nd edition)
Azami 11963