Sappāṇakavagga

Vinayapiṭaka · Parivāra · Vol. 8 · Section 355

[355] Knowingly conferring full ordination (upasampadā) upon a person less than twenty years of age, one incurs two offenses (āpatti): while conferring the ordination, there is an offense of wrong-doing (dukkaṭa) in the act; when the ordination has been completed, there is an offense entailing expiation (pācittiya).

English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.

This passage also appears in 1 other place

Vol. 8 · Section 745 — Kumārībhūtavagga