Sahih Bukhari
Accepting Information Given by a Truthful Person
Volume: 009 / Book Number: 091 / Hadith Number: 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.