俱舍論頌疏論本 27.111

27.111

有死留堅體者，有說願力留所化身亦得死後，如大迦葉留骨鎖身至慈尊世，唯堅實體可得久留，即骨鎖身名堅實也，謂簡肉等。

Regarding "some retain a solid substance upon dying": some say that by the power of a vow, one can retain an apparitional body even after death. For instance, Mahākāśyapa retained his skeleton-body until the era of Maitreya. Only a solid, substantial body can be retained for a long time; the skeleton-body is what is called 'solid,' which excludes flesh and the like.