From Sahih Muslim (Hadith 5960):
Abu Huraira reported Allah's Messenger (ﷺ) 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 and he made it complete but for one brick in one of its corners. People began to walk round it, and the building pleased them and they would say: But for this brick your building would have been perfect. Muhammad (ﷺ) said: And I am that final brick
Reference: Muslim 5960