Sahih al-Bukhari — Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi) — Hadith No: 4289
Translation
Narrated 'Abdullãh bin 'Umar (ra):Allah's Messenger (ﷺ) entered Makkah through its upper part and he was riding his she-camel. Usãma bin Zaid was his Companion-rider behind him (on the same she-camel). In his company were Bilãl and 'Uthmãn bin Talha, who was one of the Al-Hajabah (who keep the key of the gate of the Ka'bah). When he made his she-camel kneel down in the Mosque (i.e., Al-Masjid al-Haram), he ordered him (i.e., 'Uthman) to bring the key of the Ka'bah. Then Allah's Messenger (ﷺ) entered the Ka'bah along with 'Usãma bin Zaid, Bilãl and 'Uthmãn bin Talha, and he stayed in it for a long period and then came out. The people rushed (to get in) and `Abdullãh bin 'Umar was the first to enter and he found Bilãl standing behind the door. Ibn `Umar asked Bilãl, "Where did Allah's Messenger (ﷺ) offer the Salat (prayer)?" Bilãl showed him the place where he (ﷺ) had offered Salat (prayer). `Abdullah later on said, "I forgot to ask Bilãl how many prostrations (i.e., Rak'a) the Prophet offered