四分比丘戒本疏 2.12

2.12

第四、取非親尼衣戒。親者要須父母七世，開之不犯。若受戒弟子，亦是非親也。

Fourth: the precept against accepting robes from an unrelated bhikṣuṇī. "Related" strictly requires relations within seven generations through father and mother, which is permitted without offence. A disciple who has received the precepts from oneself is also considered unrelated.