四分律刪繁補闕行事鈔 3.44

3.44

《僧祇》：得敷坐。在道行，得長疊中疊，著衣囊上，左肩上擔。若至坐處，當敷而坐。若置本處，當中揜之，後徐舒而坐。凡坐法，應先手按，然後乃坐。《賢愚經》：舍利弗以尼師壇著左肩上，入眾降邪道。《鼻柰耶》多文，著肩上入山坐禪。今在左臂，定是非法。

The Mahāsāṃghika-vinaya states: It may be spread out to sit upon. When walking on the road, it may be folded lengthwise and folded in half, placed upon the robe bag, and carried on the left shoulder. When arriving at a sitting place, one should spread it out and sit. If placing it in its original location, fold it in the middle, and afterward gently unfold it and sit. For the general method of sitting, one should first press with the hand and only then sit down. The Sutra of the Wise and the Foolish states: Śāriputra placed the niṣīdāna on his left shoulder, entered the assembly, and subdued the heretics. The Vinaya [piṭaka] has many texts about placing it on the shoulder when entering the mountains to practice dhyāna. Placing it on the left arm today is definitely non-Dharmic.