Abu Nadrah narrates from Imran bin Husayn (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) stayed eighteen nights in Makkah at the time of the Conquest, and he (peace and blessings be upon him) used to pray two rak'ahs each.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5471