四分律比丘含注戒本 2.593

2.593

(The Buddha said: "If one is not yet a full twenty years of age, he cannot endure cold, heat, hunger, thirst, wind, rain, mosquitoes, gnats, poisonous insects, or harsh speech; if physical pain arises, he cannot endure it; moreover, he cannot endure maintaining the precepts or eating only one meal a day. If he has completed twenty years, he can endure such painful things as above.")