四分律刪繁補闕行事鈔 2.233

2.233

The Daśādhyāya-vinaya states: In a place without water, if there is food on the surface of water, discard the top and drink from below; if there is food at the bottom, drink from above; as for ghee, oil, and the like, blow them aside and drink. In a spring or pool, if there is food, it is also like this.
The Mahāsāṃghika-vinaya and the Sarvāstivāda-vinaya-vibhāṣā state: Having begged and eaten food, if there are leftovers, they are discarded on a rock in the wilderness; the next day, if one fails to obtain begged food and, without prior intent, returns along the original path, and the old rice remains on the rock, if there is no kappiyakāraka, one may take it oneself; parts eaten by crows or birds must be scooped away. The occasion in the Five Hundred Questions is identical to the above. The reason this is permitted is that offerings given out of faith are weighty. Furthermore, ownerless property may be taken and eaten according to the custom of Uttarakuru.
The Pañcavargika-vinaya states: A bhikṣu gave leftover fruit to a kappiyakāraka without the intention of getting it back; later the kappiyakāraka gave it back to the bhikṣu. The Buddha said: 'Once it has left the hands, it is designated pure; eat it.'