Virtue: I have never seen anyone more in the habit of smiling than the Messenger.
The Prophet Muhammad [Peace And Blessings Be Upon Him] said: "Do not abuse anyone, do not look down upon any good work, and when you speak to your brother, show him a cheerful face." [Sunan of Abu-Dawood, Hadith 1889]
Whenever the Prophet [Peace And Blessing Be Upon Him]saw me after I had embraced Islam; he would receive me with a smile. I have never seen anyone who smiles more than the Prophet.” (Al-Bukhari)
The Healthy Side of Smiling
Research has revealed that smiling lowers the heart rate and temporarily reduces blood pressure reducing stress by releasing endorphins that naturally diminish stress hormones simultaneously putting us in a better mood. Endorphins also lessen pain.
“Your smile for your brother is charity.” (At-Tirmidhi, 1879)
Reference: At-Tirmidhi