Duty of a family priest
Srimad-Bhagavatam
SB Canto 9
It is the duty of a family priest not to curse a disciple but to give him relief through the performance of some sort of atonement
SB 9.2.9, Tanslation and Purport: Although Prsadhra had committed the sin unknowingly, his family priest, Vasistha, cursed him, saying, "In your next life you shall not be able to become a ksatriya. Instead, you shall take birth as a sudra because of killing the cow."
It appears that Vasistha was not free from tamo-guna, the mode of ignorance. As the family priest or spiritual master of Prsadhra, Vasistha should have taken Prsadhra's offense very lightly, but instead Vasistha cursed him to become a sudra. It is the duty of a family priest not to curse a disciple but to give him relief through the performance of some sort of atonement. Vasistha, however, did just the opposite. Therefore Srila Visvanatha Cakravarti Thakura says that he was durmati; in other words, his intelligence was not very good