Sahih Muslim
The Book Pertaining to the Excellent Qualities of the Holy Prophet (may Peace be upon them) and His Companions (Kitab Al-Fadail)
Book Number: 030 / Hadith Number: 5675
Abu Hurairh reported Allah's Messenger (may peace be upon him) as saying: The similitude of mine and that of the Apostles before me is that of a person who built a house quite imposing and beautiful, but for one brick in one of its corners. People would go round it, appreciating the building, but saying: Why has the brick not been fixed here? He said: I am that brick and I am the last of the Apostles.