Majjhima Nikaya 3:109
SUJATOYasmiṁ samaye, bhikkhave, bhikkhuno upaṭṭhitā sati hoti asammuṭṭhā, satisambojjhaṅgo tasmiṁ samaye bhikkhuno āraddho hoti. Satisambojjhaṅgaṁ tasmiṁ samaye bhikkhu bhāveti, satisambojjhaṅgo tasmiṁ samaye bhikkhuno bhāvanāpāripūriṁ gacchati.
At such a time, a mendicant has activated the awakening factor of mindfulness; they develop it and perfect it.