SB 7.10.22
kuru tvam preta-krtyani
pituh putasya sarvasah
mad-anga-sparsanenanga
lokan yasyati suprajah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
My dear child, your father has already been purified just by the touch of My body at the time of his death. Nonetheless, the duty of a son is to perform the sraddha ritualistic ceremony after his father’s death so that his father may be promoted to a planetary system where he may become a good citizen and devotee.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
In this regard, Srila Visvanatha Cakravarti Thakura says that although Hiranyakasipu was already purified, he had to take birth on a higher planetary system to become a devotee again. Prahlada Maharaja was advised to perform the ritualistic ceremony as a matter of etiquette, for the Supreme Personality of Godhead under no circumstances wants to stop the regulative principles. Madhva Muni also instructs:
madhu-kaitabhau bhakty-abhava
durau bhagavato mrtau
tama eva kramad aptau
bhaktya ced yo harim yayau
When the demons Madhu and Kaitabha were killed by the Supreme Personality of Godhead, their kinsmen also observed the ritualistic ceremonies so that these demons could return home, back to Godhead.