Sahih Muslim Book 001, Hadith Number 0429.
Chapter : This Ummah (Ummah of Islam) would constitute half of the inhabitants of Paradise.
Abdullah b Mas'ud reported: The Messenger of Allah (may peace be upon him) addressed us and then supported his back (by reclining) against a leather tent and said: Behold, no one but a believing person would enter Paradise. O Allah, (see) have I conveyed (it not)? O Allah, be witness (to it that I have conveyed it). (Then addressing the companions) he said: Don't you like that you should constitute one-fourth of the inhabitants of Paradise? We said: Yes, Messenger of Allah. He again said: Don't you like that you should constitute one-third of the inhabitants of Paradise? They said: Yes, Messenger of Allah. He said: I hope that you would constitute one- half of the inhabitants of Paradise and you would be among the peoples of the world, like a black hair on (the body of) a white ox or like a white hair on the body of a black ox.