Saṁmappadhānavibhaṅgasuttantabhājanīya

Abhidhammapiṭaka · Vibhaṅga · Vol. 35 · Section 470

[470] "Exerts the mind (citta)": herein, what is the mind? That which is mind, mentality (mano), mentation (mānasa), … the corresponding mind-consciousness element (tajjā manoviññāṇadhātu) — this is called the mind. He exerts, thoroughly exerts, supports, and reinforces this mind. Therefore it is said, "exerts the mind."

English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.

This passage also appears in 2 other places

Vol. 35 · Section 499 — Abhidhaṁbhājanīya
Vol. 35 · Section 488 — Abhidhaṁbhājanīya