Srimad Bhagavatam Canto 03, Chapter 20, Text 43

SB 3.20.43

ta atma-sargam tam kayam
 pitarah pratipedire
sadhyebhyas ca pitrbhyas ca
 kavayo yad vitanvate
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
The Pitas themselves took possession of the invisible body, the source of their existence. It is through the medium of this invisible body that those well versed in the rituals offer oblations to the Sadhyas and Pitas [in the form of their departed ancestors] on the occasion of sraddha.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
Sraddha is a ritualistic performance observed by the followers of the Vedas. There is a yearly occasion of fifteen days when ritualistic religionists follow the principle of offering oblations to departed souls. Thus those fathers and ancestors who, by freaks of nature, might not have a gross body for material enjoyment can again gain such bodies due to the offering of sraddha oblations by their descendants. The performance of sraddha, or offering oblations with prasada, is still current in India, especially at Gaya, where oblations are offered at the lotus feet of Visnu in a celebrated temple. Because the Lord is thus pleased with the devotional service of the descendants, by His grace He liberates the condemned souls of forefathers who do not have gross bodies, and He favors them to again receive a gross body for development of spiritual advancement.
Unfortunately, by the influence of maya, the conditioned soul employs the body he gets for sense gratification, forgetting that such an occupation may lead him to return to an invisible body. The devotee of the Lord, or one who is in Krsna consciousness, however, does not need to perform such ritualistic ceremonies as sraddha because he is always pleasing the Supreme Lord; therefore his fathers and ancestors who might have been in difficulty are automatically relieved. The vivid example is Prahlada Maharaja. Prahlada Maharaja requested Lord Nrsimhadeva to deliver his sinful father, who had so many times offended the lotus feet of the Lord. The Lord replied that in a family where a Vaisnava like Prahlada is born, not only his father but his father’s father and their fathers — up to the fourteenth father back — are all automatically delivered. The conclusion, therefore, is that Krsna consciousness is the sum total of all good work for the family, for society and for all living entities. In the Caitanya-caritamrta, the author says that a person fully conversant with Krsna consciousness does not perform any rituals because he knows that simply by serving Krsna in full Krsna consciousness all rituals are automatically performed.
Srimad Bhagavatam Canto 03, Chapter 20, Text 42
Srimad Bhagavatam Canto 03, Chapter 20, Text 44