(16) CHAPTER. The Statement of Allah ” … And eat and drink until the white thread (light) of dawn appears to you distinct from the black thread (darkness of night), then complete your Saum (fast) till the nightfall…” (V.2:187) Narrated Al-Bara: The Prophet, peace be upon him, said as above.
1916. Narrated ‘Adi bin Hatim: When the following Verses were revealed: “Until the white thread appears to you distinct from the black thread, I took two (hair) strings, one black and the other white, and kept them under my pillow and went on looking at them throughout the night but could not make anything out of it. So, the next morning I went to Allah’s Messenger, peace be upon him, and told him the whole story. He explained to me, “That Verse means the darkness of night and the whiteness of dawn.”