四分律行事鈔資持記 2.786

2.786

五中。乘乘戒，出〈雜犍度〉；彼因六群輒乘象馬車乘，佛制不應；後諸老病比丘不能行，不敢乘騎；佛因開之，如文所引。上乘字平呼，下去呼。男乘立車，女乘坐車，尼騎即草馬。〈瞻病〉中云：至道逢病比丘，求車乘載歸，不問㹀牛草馬等。《僧祇》無病通制。暫趁行船，有緣故也。

Regarding the fifth [case]: the precept against riding in vehicles comes from the "Miscellaneous Skandhaka." There, because the group of six bhikṣus rode in elephant, horse, and carriage vehicles without restraint, the Buddha prohibited it as inappropriate; later, elderly and sick bhikṣus who were unable to walk did not dare to ride, so the Buddha granted an exception on their account, as cited in the text. The first word cheng is read in the level tone, and the second in the falling tone. Men ride in standing carts, women ride in sitting carts, and for bhikṣuṇīs riding means riding mares. The "Attending the Sick" section states: if coming upon a sick bhikṣu on the road, one should seek a vehicle to carry him back, without asking whether it is a cow, a mare, etc. The Mahāsāṃghika-vinaya prohibits it generally in the absence of illness. Temporarily taking a boat is permitted because there is an exigent reason.