四分律比丘含注戒本 3.60

3.60

不犯者：或臍中生瘡，下著；若膝[跳-兆+專]有瘡，高著。若僧伽藍內，若村外，若作時，若行道者，無犯。

As for non-offense: if sores develop on the navel, one wears it low; if there are sores on the knees or shins, one wears it high. Inside the saṃghārāma, outside the village, while working, or while walking on the road, there is no offense.