an.3.43 Aṅguttara Nikāya (Numbered Discourses)

“Bhikkhus, when one sees three advantages, it is enough to teach others the Dhamma. What three? (1) The one who teaches the Dhamma experiences the meaning and the Dhamma. (2) The one who hears the Dhamma experiences the meaning and the Dhamma. (3) Both the one who teaches the Dhamma and the one who hears the Dhamma experience the meaning and the Dhamma. Seeing these three advantages, it is enough to teach others the Dhamma.”