Sahih Muslim Book 7, Hadith Number 2756.

Chapter : Permissibility of entering into the state Ihram conditionally due to illness.

‘Aisha (Allah be pleased with her) reported that Allah’s Messenger (may peace be upon him) went (into the house of) Duba’a bint Zubair and said to her: Did you intend to perform Hajj? She said: By Allah, (I intend to do so) but I often remain ill, whereupon he (the Holy Prophet) said to her: Perform Hajj but with condition, and say: O Allah, I shall be free from Ihram where you detain me. And she (Duba’a) was the wife of Miqdad.