Sayyiduna ‘Adi bin Hatim (may Allah be pleased with him) narrates that when this verse was revealed: {وَکُلُوْا وَاشْرَبُوْا حَتّٰییَتَبَیَّنَ لَکُمُ الْخَیْطُ الْاَبْیَضُ مِنَ الْخَیْطِ الْاَسْوَدِ مِنَ الْفَجْرِ} … And eat and drink until the white thread becomes distinct to you from the black thread of dawn (Surah Al-Baqarah: 187), I, ‘Adi, took two threads, one black and the other white, and placed them under my pillow. Then I began to look at them, but neither the black thread nor the white thread became distinct to me. When morning came, I went to the Noble Prophet (peace and blessings be upon him) and told him what I had done. The Prophet (peace and blessings be upon him) said: "Your pillow is indeed very wide! What is meant is the whiteness of the day and the darkness of the night."

It is also narrated from Sayyiduna ‘Adi (may Allah be pleased with him), he says: The Noble Prophet (peace and blessings be upon him) taught me about prayer and fasting, and he (peace and blessings be upon him) said: At such-and-such time, perform such-and-such prayer and keep the fast; when the sun sets, then eat and drink, until the white thread becomes distinct from the black thread, and keep fasts for thirty days, unless the moon is sighted earlier. I took two threads, one black and one white, and began to look at them, but they did not become distinct for me. When I mentioned this to the Noble Prophet (peace and blessings be upon him), he smiled and said: O Ibn Hatim! By this is meant the whiteness of the day and the darkness of the night.