SB 7.10.22

kuru tvaṁ preta-kṛtyāni
 pituḥ pūtasya sarvaśaḥ
mad-aṅga-sparśanenāṅga
 lokān yāsyati suprajāḥ
Synonyms: 
kuru — perform; tvam — you; preta-kṛtyāni — the ritualistic ceremony performed after death; pituḥ — of your father; pūtasya — already purified; sarvaśaḥ — in all respects; mat-aṅga — My body; sparśanena — by touching; aṅga — My dear child; lokān — to planets; yāsyati — he will be elevated; su-prajāḥ — to become a devotee-citizen.
Translation: 
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 śrāddha 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: 

In this regard, Śrīla Viśvanātha Cakravartī Ṭhākura says that although Hiraṇyakaśipu was already purified, he had to take birth on a higher planetary system to become a devotee again. Prahlāda Mahārāja 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-kaiṭabhau bhakty-abhāvā
 dūrau bhagavato mṛtau
tama eva kramād āptau
 bhaktyā ced yo hariṁ yayau

When the demons Madhu and Kaiṭabha 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.