Sahih Bukhari Volume 009, Book 092, Hadith Number 451.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 92. Holding Fast to the Qur'an and Sunnah
Narrated By '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, otherwise 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 Said 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."