Narrated 'Ubai bin `Umar: Abu Musa asked permission to enter upon `Umar, but seeing that he was busy, he went away. `Umar then said, Didn't I hear the voice of `Abdullah bin Qais? Allow him to come in. He was called in and `Umar said to him, What made you do what you did. He replied, We have been instructed thus by the Prophet `Umar said, Bring proof (witness) for this, other wise I will do so-and-so to you. Then `Abdullah bin Qais went to a gathering of the Ansar who then said, None but the youngest of us will give the witness for it. So Abu Sa`id Al-Khudri got up and said, We used to be instructed thus (by the Prophet). `Umar said, This tradition of the Prophet remained hidden from me. Business in the market kept me busy.