Musnad Ahmad 30:1975

Husayn narrated to us, al-Mas'udi narrated to us, from Dawud Abu Yazid, from his father, from Abu Hurayrah, that the Prophet, peace and blessings of Allah be upon him, said: "The thing that causes a person to enter the Fire the most is the two hollows: the mouth and the private parts. And the thing that causes a person to enter Paradise the most is the fear of Allah, the Almighty and Majestic, and good character."