Musnad Abu Ya'la al-Mawsili 243:54

Abu Bakr narrated to us, Mu'alla ibn Mansur narrated to us, from Musa ibn A'yan, from 'Abdullah ibn Muhammad ibn 'Aqil, from Sulayman ibn Yasar, from 'Aqil, the freed slave of Ibn 'Abbas, from Abu Musa, who said: I and Abu al-Darda' were with the Messenger of Allah, may Allah bless him and grant him peace, and he said: "Whoever protects what is between his two jaws and his two legs will enter Paradise."