Hakam bin A'raj says that once I was present in the service of Sayyiduna Ibn Abbas (may Allah be pleased with them). I asked him to tell me something about the Day of Ashura. He said: When you see the crescent of Muharram, keep counting its dates. When the morning of the ninth day comes, observe the fast. I asked: Did the Prophet (peace and blessings be upon him) fast in this manner? He replied: Yes.