Do not belittle any good deed
Abu Dharr al-Ghifāri (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "Do not belittle any good deed, even meeting your brother with a cheerful face."
It is highly recommended, according to this Hadīth, to meet people with a cheerful face. This is a good deed that Muslims should observe and appreciate. It reflects friendliness and cordiality toward others, and it makes them happy.