Aṅguttara Nikāya 3.135 14. Yodhājīvavagga Mittasutta

“Tīhi, bhikkhave, aṅgehi samannāgato mitto sevitabbo.

“Mendicants, you should associate with a friend who has three factors.

Katamehi tīhi? (…)

What three?

Duddadaṁ dadāti, dukkaraṁ karoti, dukkhamaṁ khamati—

They give what is hard to give, they do what is hard to do, and they endure what is hard to endure.

imehi kho, bhikkhave, tīhi aṅgehi samannāgato mitto sevitabbo”ti.

You should associate with a friend who has these three factors.”

Tatiyaṁ.