Bahudhātukasutta

mn115:4.1 “But sir, how is a mendicant qualified to be called ‘skilled in the elements’?”

mn115:4.2 “There are, Ānanda, these eighteen elements.

mn115:4.3 The eye element, sight element, and eye consciousness element.

mn115:4.4 The ear element, sound element, and ear consciousness element.

mn115:4.5 The nose element, smell element, and nose consciousness element.

mn115:4.6 The tongue element, taste element, and tongue consciousness element.

mn115:4.7 The body element, touch element, and body consciousness element.

mn115:4.8 The mind element, ideas element, and mind consciousness element.

mn115:4.9 When a mendicant knows and sees these eighteen elements,

mn115:4.10 they’re qualified to be called ‘skilled in the elements’.”