Acharanga Bhasyam: Verse 14

9.4.14 avi jhāti se mahāvīre, āsaṇatthe akukkue jhāṇaṃ.
uḍḍhamahe tiriyaṃ ca, pehamāṇe samāhimapaḍiṇṇe..

And Mahāvīra meditated sitting in the postures like 'ukkudu' without distraction. He meditated concentrating on objects above, below, and in front, without any pre-made resolve.

Bhāṣyaṃ Verse 14

Now, the meditational posture of the Lord is described. The Lord engaged himself in meditation, being seated in the proper posture. The principle postures are the 'ukkuḍu' posture, hero's posture, milking posture and standing posture etc. By the word 'akukkue' the posture of relaxation (abandonment of the body) or the steadiness of the body is indicated. By the word meditation, contemplation on reality or white (or the highest kind of) meditation is implied. The words upper, lower etc. are mentioned with reference to the local target of meditation. The Lord meditated upward in order to concentrate on the objects lying in the upper region. He meditated down-wards in order to concentrate on the objects lying in the lower region. He meditated horizontally in order to concentrate on the objects lying in the horizontal region. ^[1]

Having become free from pre-made resolve, the Lord perceived in meditation the ecstasy, or he meditated on upward, downward or horizontal parts of the body by perceiving in meditation the ecstasy.

For similar description, see 2.125.