Majjhima Nikaya 3:121
SUJATOYasmiṁ samaye, bhikkhave, bhikkhu tathāsamāhitaṁ cittaṁ sādhukaṁ ajjhupekkhitā hoti, upekkhāsambojjhaṅgo tasmiṁ samaye bhikkhuno āraddho hoti, upekkhāsambojjhaṅgaṁ tasmiṁ samaye bhikkhu bhāveti, upekkhāsambojjhaṅgo tasmiṁ samaye bhikkhuno bhāvanāpāripūriṁ gacchati.
At such a time, a mendicant has activated the awakening factor of equanimity; they develop it and perfect it.