The Noble Quran was not revealed all at once, but was rather revealed to the Prophet ﷺon different occasions, and some ayaat were revealed to further explain and clarify others. The Companions(may Allah be pleased with them)hastened to comply with the divine commands revealed to them. In this hadeeth, Sahl ibn Sa‘d (may Allah be pleased with him) related the occasion during which the following ayah was revealed. Allah, Exalted is He, Says (what means): {And eat and drink until the white thread becomes distinct to you from the black thread.} [Quran 2:187].Some of the Companions (may Allah be pleased with them)understood the wording of the ayah literally, and that it meant actual white and black threads. Therefore, they would bring two threads (a black and a white one) and tie them to their feet and would eat and drink until they were able to differentiate between the black and white one (i.e., to determine the beginning of the fast day after dawn). Afterwards, Allah, Exalted is He, revealed the words {of the dawn} [Quran 2:187].in the ayah, and thereupon they learned that it does not referto actual white and black threads, but rather meant the ability to distinguish the blackness of the night from the whiteness of the morning, i.e., after dawn, and that the break of dawn was the time limit for the end of the night and the beginning of the morning. This means that whoever wishes to observe fasting is required to abstain from eating and drinking upon seeing that clear and prominent sign, i.e., the break of dawn. .