Sayyiduna Hudhayfah (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "Do not proceed beyond this month (Ramadan) until you see the moon or complete the counting (of Sha'ban)."

Hazrat Simak narrates that I came to Sayyiduna Ikrimah on the day when there was doubt about the beginning of Ramadan, while he was eating food. So he said, "Come closer and eat food." I said, "I am fasting." He said, "By Allah, you will certainly come closer (and eat)." I said, "Then please explain this to me." He said, "Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrated to us that the Messenger of Allah (peace and blessings be upon him) said: 'Do not welcome Ramadan (by fasting) before it. Fast when you see the moon and break your fast when you see the moon. Then if clouds or mist come between you and the sighting of the moon, then complete the counting (of Sha'ban) to thirty days.'"