Mitta Sutta (AN 3:136)
“Monks, a friend endowed with three factors is worth associating with. Which three? He/she1 gives what is hard to give, does what is hard to do, endures what is hard to endure. A friend endowed with three factors is worth associating with.”
1. Following the Thai, Sri Lankan, and Burmese editions. The PTS edition inserts here, idha bhikkhave bhikkhu, “Monks, there is the case where a monk…” The parallel passage at AN 7:35 doesn’t add the stipulation that a friend has to be a monk, and there seems no reason to add it here.