He was a Sākiyan and entered the Order when the Buddha visited his kinsmen at Kapilavatthu. For some time he was the Buddha’s personal attendant—e.g., when the Buddha breached the Mahāsīhanāda Sutta. MN.i.83

One day, when entering the city for alms, he saw a nautch girl gaily dressed, dancing to the accompaniment of music and contemplated her as the snare of Māra. Making this his topic of thought, he developed insight into the perishableness of life and became an arahant. Thag.267–270 Another day, while walking with the Buddha, they came to a cleft in the road, and the Buddha wished to go along one way, while Nāgasamāla wished to go along another, in spite of the Buddha’s warning that it was dangerous. In the end, he put the Buddha’s begging bowl and robe on the ground and left him. Brigands waylaid him and ill treated him, breaking his bowl and threatening to kill him. Thereupon he turned back to the Buddha and asked his forgiveness. Ud.viii.7