Musnad Abu Ya'la al-Mawsili 252:31

Al-Qawariri narrated to us, Fudayl ibn Sulayman al-Numayri narrated to us, Abu Hazim narrated to us, Sahl ibn Sa’d narrated, saying: When this verse was revealed: "And eat and drink until the white thread becomes distinct to you from the black thread," a man would take a white thread and a black thread and eat until he could distinguish between them. Until Allah, the Mighty and Majestic, revealed: "of the dawn," and thus clarified that.