In the Brahmpuran, it is said that in the dark fortnight (Krishna Paksha) of Ashvin (This year from Tue, 5 September 2017 to Tue, 19 September 2017), Yama frees all souls so that they can visit their children to accept the food they offer at the shraddh ceremony.
Those who do not offer food to their forefathers during this period attract wrath and many have to suffer if cursed by them. Coming generations may suffer on account of this lapse. It is also customary to perform shraddh on the death anniversary of the deceased. The ceremony aims at feeding Brahmins until they are content.
In the Manusmriti, 3/275, it is written:
“Whatever one offers ceremoniously and with devotion to the deceased reaches them in heaven in imperishable and eternal form”.
In the Garudapuran it is said:
“When shraddh is performed to their satisfaction, the deceased bless successors with age, a son, fame, salvation, heaven, glory, stability, strength, prosperity, cattle, happiness, money, growth and eternal blessings”.
In the Yamsmriti, 36-37, it is said:
“A father, grandfather and great grandfather desire the shraddh ceremony just as birds living on trees desire that the tree bear fruit. They expect that successors will offer honey, milk and kheer (rice-porridge) at the shraddh ceremony”.
In the Yamsmriti, 40, it is further said:
“Whatever number of morsels a Brahmin, expert in mantras, eats, that many morsels are accepted by the father of the person performing shraddh by being present within the body of the Brahmin“.
Purnima Tithi's Shraddh: Tue, 5 September 2017
Sarv Pitra Amavasya Shraddha: Tue, 19 September 2017