Chandasutta

Suttapiṭaka · Saṁyuttanikāya · Mahāvaggasaṁyutta · Vol. 19 · Section 808

[808] … He dwells contemplating the mind in the mind (citta), ardent, clearly comprehending, mindful, having removed covetousness and grief regarding the world. As he dwells contemplating the mind in the mind, whatever desire (chanda) there is in regard to the mind is abandoned; through the abandoning of that desire, the Deathless (amata) is realized.

English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.

This passage also appears in 2 other places

Vol. 19 · Section 1268 — Rahogatavagga
Vol. 19 · Section 707 — Sūdasutta