Hadith 123
قرا رسول الله صلى الله عليه وسلم ”هل جزاء الاحسان الا الاحسان“ وقال : هل تدرون ما قال ربكم؟ قالوا : الله و رسوله اعلم ، قال : يقول : هل جزاء من انعمت عليه بالتوحيد الا الجنة
The Messenger of Allah (peace and blessings be upon him) recited this verse: "Is the reward for good anything but good?" and said, "Do you know what your Lord has said?" The companions replied, "Allah and His Messenger know best." He (peace and blessings be upon him) said: "Allah Almighty says that for the one upon whom I have bestowed the blessing of monotheism, the only reward is Paradise."