Walimah is only in five occasions: in the 'Urs, Khurs, 'Idhar, Wikar and the Rikaz – 'Urs is when a person gets married; and Khurs is when a child is born; and 'Idhar is on the circumcision of a baby boy; and Wikar is when a person purchases a house; and Rikaz is when a person returns from Hajj.

Biharul Anwar, Volume 96, Page 384 - Shi'ite Hadith