Accepting Information Given by a Truthful Person

Bukhari :: Book 9 :: Volume 91 :: Hadith 368

Narrated 'Umar:

I came and behold, Allah's Apostle was staying on a Mashroba (attic room) and a black slave of Allah's Apostle was at the top if its stairs. I said to him, "(Tell the Prophet) that here is 'Umar bin Al-Khattab (asking for permission to enter)." Then he admitted me.