Collection of Hadith

695. Abu Dharr (May Allah be pleased with him) reported: Messenger of Allah (PBUH) said, "Do not disdain a good deed, (no matter how small it may seem) even if it is your meeting with your (Muslim) brother with a cheerful face.''
[Muslim].

Ibn Jaz said: “I have not seen anyone who smiled more than the Messenger of Allah (sal Allahu alaihi wa sallam).” (Hasan) [Chapters on Al-Manaqib: Jami At-Tirmidhi]