Musnad Abu Ya'la al-Mawsili 150:181

Abu Kurayb narrated to us, Sa'id ibn Sharhabil narrated to us, from Layth ibn Sa'd, from Khalid ibn Yazid, from Sa'id ibn Abi Hilal, from Ibn 'Abbas, from 'A'ishah, who said: I heard the Messenger of Allah, may Allah bless him and grant him peace, while he was addressing the people, saying: "Your place in Paradise [is guaranteed]—meaning for whoever guards what is between his two jaws and guards what is between his two legs."