Sayyiduna ‘Adi bin Hatim Tai says: The Messenger of Allah, peace and blessings be upon him, taught me about prayer and fasting, and he, peace and blessings be upon him, said: Perform such-and-such prayers and fast in this manner. When the sun sets, you may eat and drink throughout the night, until the white thread becomes distinct from the black thread, and complete the full thirty fasts of (Ramadan), unless the moon is sighted before that. So I took a black thread and a white thread and began to look at them (at the time of suhoor), but they were not becoming clear to me. Therefore, I informed the Messenger of Allah, peace and blessings be upon him, about this. Upon hearing this, he, peace and blessings be upon him, smiled and said: By the white thread is meant the whiteness of the day becoming distinct from the darkness of the night at the time of dawn.