When his ordination was but one year old, he ordained another bhikkhu, to increase the number of holy ones, and went with him to wait upon the Buddha. The Buddha roundly rebuked him for this hasty procedure. Vin.i.59 Later the Buddha declared Upasena to be the best of those who were altogether charming (samantapāsādikānaṃ). AN.i.24 He visited the Buddha when the Buddha had enjoined on himself a period of solitude for a fortnight; the monks had agreed that anyone who went to see the Buddha would be guilty of a pācittiya offence, but the Buddha, desiring to talk to him, asked one of Upasena’s followers if he liked rag-robes. “No, Sir, but I wear them out of regard for my teacher,” was the reply. Vin.iii.230ff.
In the Theragāthā are found several verses ascribed to Upasena as having been spoken by him in answer to a question by his student, regarding what was to be done during the dissensions of the Kosambī monks Thag.577–586 The Udāna states Ud.p.45f. that once when he was taking his siesta he reviewed the happiness he enjoyed and the glories of the life he led under the guidance of the Buddha. The Buddha, noticing this, proclaimed his approval.
One day, while Upasena was sitting after his meal in the shadow of the Sappasondika-pabbhāra, fanned by the gentle breeze, mending his outer robe, two young snakes were sporting in the tendrils overhanging the cave. One fell on his shoulder and bit him, and the venom spread rapidly throughout his body; he called to Sāriputta and other monks who were near, and requested that he might be taken outside on a couch, there to die. This was done, and his body “was scattered there and then like a handful of chaff.”. SN.iv.40f.