Personalities of the Buddhist Suttas
(DPPN: He was born in Nalaka as the son of Rupasari, the brahminee, his father being Vanganta. He was the younger brother of Sariputta. When he came of age, he learnt the three Vedas, and, having heard the Buddha preach, entered the Order. 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, and Upasena, wishing to earn the Master's praise on account of the very cause of this rebuke, practiced insight and became an arahant. Thereafter he adopted various dhutangas [austerities] and persuaded others to do likewise. In a short time he had a large retinue, each member of which was charming in his way, and the Buddha declared Upasena to be the best of those who were altogether charming (samantapasadikanam). Buddhaghosa says that Upasena was famed as a very clever preacher and many joined him because of his eloquence.
One day, while Upasena was sitting after his meal in the shadow of [his residence in a cave] 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 Sariputta 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." [S.iv.40f.]
From the Psalms:
[one time] he was asked [by some bhikkhu] ... what was to be done during the dissentions and the schism [at Kosambī — Vin ii,312; M., i. 320 ff]. Upasena taught him thus:
Lonely the spot and far away where noise
Scarce comes, the haunt of creatures of the wild:
'Tis there the Brother should his couch prepare
For purposes of studious retreat.
From rubbish-pile, or from the charnel-field,
Or from the highways let him take and bring
Worn clothes and thence a cloak of patchwork make,
And in such rough apparel clothe himself.
In lowliness of mind from house to house,
In turn unbroken [not picking and choosing which house--mo] let the Brother fare
Seeking his alms, sense guarded, well controlled;
With any fare content rough though it be,
Nor fain for other than he gets, or more,
For if he once indulge in greed for tastes,
Ne'er can his mind in jhana take delight.
In great content, with very sparse desires,
Remote, secluded: so the sage should live,
Detached from housefolk and the homeless, both.
Let him so show himself as he were dull
And dumb, nor let the wise man speech prolong
Unduly, when in midst of gathered folk.
Let him not any man upbraid; let him
Refrain from hurting; let him be in rule
And precept trained, and temperate in food.
Let him be one who concentrates upon
The symbol, skilled in genesis of thought.
To practice Calm let him devote himself,
And Intuition also in due time.
With energy and perseverance armed,
Let him be ever to his studies yoked;
Nor till he have attained the end of Ill,
Let the wise man go forth in confidence.
Thus if the Brother, fain for purity
[Of knowledge and of vision] shall abide,
The working of th' Intoxicants shall cease,
And he shall reach and find Nibbana's peace.
["Let him be one who concentrates upon
The symbol, skilled in genesis of thought."
Although I do not have the Pali for this, my assumption is that "The Symbol" is "nimmita", mark, or sign; which would be, ultimately, although perhaps through a "concentration device", "change," "not selfness," and "Pain," observing how reactions to the sensations produced by these phenomena started up grasping thoughts.]