Abdur Rahman bin Zaid bin Khattab says: I delivered a sermon on a day about which there was doubt as to whether it was Sha'ban or Ramadan. I said: I have sat with the noble Companions and asked them questions; they informed me that the Messenger of Allah, peace and blessings be upon him, said: Begin fasting upon sighting the moon and stop fasting upon sighting the moon, and perform other acts of worship accordingly. If, for some reason, the moon is concealed, then complete thirty days, and if two Muslims bear witness to the sighting or non-sighting of the moon, then begin or stop fasting on that basis.