四分律比丘含注戒本 3.263

3.263

不犯者：有病；或食中有草有蟲，或手有不淨，振去之；或有未受食，手觸而污，手振去之。

There is no offense for: one who is ill; or if there is grass or an insect in the food, or if there is impurity on the hands, and one shakes it off; or if there is unreceived food that has touched and soiled the hand, and one shakes it off with the hand.