四分律比丘含注戒本 2.135

2.135

不犯中，如上方便已，在界外水陸道斷，命、梵等緣者開。

(Regarding non-offense: if one has made the above preparations, but while outside the boundary water or land routes are cut off, or because of conditions concerning life, chastity, and so forth, it is permitted.)