四分律比丘含注戒本 3.405

3.405

佛在舍衛。比丘在大樹上受夏安居，於樹上大小便。神瞋，伺便欲斷命根。比丘以過白佛，因制不得樹上安居，及繞樹大小便。若先有大小便處，聽。

The Buddha was in Śrāvastī. A bhikṣu undertook the vassa dwelling atop a large tree and defecated and urinated from atop the tree. The tree-spirit was enraged and watched for an opportunity, wishing to cut off his life-faculty. The bhikṣu reported the fault to the Buddha. Because of this, [the Buddha] formulated [the rule] that one must not undertake the vassa on a tree, nor defecate or urinate around a tree. If there was already a place for defecation and urination beforehand, it is permitted.