佛說盂蘭盆經疏 2.69

2.69

At that time, the Buddha instructed the saṅgha of the ten directions all first to recite verses of incantation and vow for the donor's household, to make vows for the parents of seven lifetimes, and to focus their minds in dhyāna-concentration, and only then receive the food. When first receiving the food, it should first be placed before the Buddha in the pagoda or monastery. After the saṅgha has finished reciting the incantation and vow, they may then partake of the food themselves.