成唯識論述記 1.214

1.214

述曰：顯不定因，謂身若大，我量便舒，身若小時，我量便卷，如一牛皮日乾水漬，日炙便卷，水濕便舒，此即無慚之類計也，謂尼虔子。今言「昵楗陀弗咀羅」，翻為「離繫子」，苦行修勝，因名為離繫。露形，少羞恥，亦名無慚。本師稱「離繫」，是彼門徒，名之為「子」。

The Commentary states: This reveals the reason for its indefiniteness: it means that if the body is large, the measure of the self expands; when the body is small, the measure of the self contracts; like an ox-hide dried in the sun and soaked in water: when scorched by the sun it contracts, and when moistened by water it expands. This is the assertion of the "shameless" class, meaning the Nirgranthas. Now "Nirgranthaputra" is translated as "sons of the Unbound." Because they practice superior austerities, they are therefore named "Unbound." They go naked and have little shame; they are also called "shameless." The original teacher was called "the Unbound"; being his disciples, they are named his "sons."