成唯識論了義燈 2.97

2.97

然二十部中，西山住、北山住、制多山，三部同云：和上不清淨亦得戒。故律云：但牒僧眾乞戒不云和上。因何此之三部作此計耶？以三先是外道之侶，見無利養，皆來共僧同住，後時俗人，由欲簡擇，在後皆剃頭，又被國王皆欲簡擇，不受戒者，皆不許住。此諸人皆云我受戒，眾僧同責，於何人邊受？自指同類以為和上，眾人即云：汝和上不清淨，云何得戒耶？遂起此計，餘十七部皆不許之，要須清淨，明捨中。

However, among the twenty schools, three schools—the Aparaśaila, Uttaraśaila, and Caityasaila—unanimously maintain that even if an upādhyāya is impure, one still obtains the precepts. Thus the Vinaya states: 'One only mentions the saṃgha to beg for the precepts, and does not mention an upādhyāya.' Why did these three schools form this view? Because these three [groups] were originally followers of tīrthikas; seeing that there were no material offerings, they all came to dwell together with the saṃgha. Later, laypeople, wishing to screen [monks], had all those behind them shave their heads. Furthermore, the king also wished to screen [them], and whoever did not receive the precepts was not permitted to stay. All these people said, 'I have received the precepts.' The assembly of monks questioned them collectively: 'From whose presence did you receive them?' They pointed to their own kind as their upādhyāya. The assembly then said: 'Your upādhyāya is impure; how could you obtain the precepts?' Thereupon they generated this view. The remaining seventeen schools all disallow it, holding that [the preceptor] must be pure, as clarified in [the section on] relinquishment.