Sahih Muslim
The Book on General Behaviour (Kitab Al-Adab)
Book Number: 025 / Hadith Number: 5363
Jabir b. Abdullah reported: I came to Allah's Apostle (may peace be upon him) and called him (with a view to seeking permission). whereupon Allah's Apostle (may peace be upon him) said: Who is it? I said: It is I. Thereupon he (the Holy Prophet) came out saying: It is I. it is I.