It has been narrated from al-Ridha ['Ali ibn Musa] (peace be upon him) that:
“…and this is a day( day of ghadir khum ) of congratulations and felicitations in which you should greet and congratulate one another. When a believer meets another, one should say, ‘All praise belongs to Allah who has made us amongst those who hold firm to the Wilayat of the Commander of the Faithful and the A’immah (prayers be upon all of them); and this is a day of smiling at other people and those of true faith.”
Iqbal al-A'mal, Page 464