Sahih Muslim
The Book of Marriage (Kitab Al-Nikah)
Book Number: 008 / Hadith Number: 3447
Umm Salama (Allah be pleased with her) reported that Allah's Messenger (may peace be upon him) married her, and he (the narrator) made mention of so many things in this connection (and one of them was this) that he said: If you desire that I spend a week with you, I shall have to spend a week with my (other) wives, and if spend a week with you, I shall have to spend a week with my (other) wives.