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: 5737
This hadith has been narrated on the authority of Jabir b. 'Abdullah through different chains of transmitters and the words are:" That the Messenger of Allah (may peace be upon him) said: He who shows no mercy to the people, Allah, the Exalted and Glorious, does not show mercy to him."