Sahih Bukhari Volume 002, Book 026, Hadith Number 692.
Narated By Um Salama : (The wife of the Prophet) I informed Allah's Apostle (about my illness). (Through other sub-narrators, Um Salama narrated that when Allah's Apostle was at Mecca and had just decided to leave (Mecca) while she had not yet done Tawaf of the Kaba (and after listening to her). The Prophet said, "When the morning prayer is established, perform the Tawaf on your camel while the people are in prayer." So she did the same and did not offer the two Rakat of Tawaf until she came out of the Mosque.