Abu Dharr (May Allah be pleased with him) reported:
Messenger of Allah (ﷺ) 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]. (ID)
App reference (ID): Book 2, Hadith 15 (ID)
Arabic/English book reference (ID): Book 2, Hadith 695 (ID)