Yājñavalkya Śikṣā 202

202

yamānvidyādayaspiṇḍāntsāntasthāndārupiṇḍavat
antasthaṃ yamavarjantu ūrṇāpiṇḍaṃ vinirdiśet

One should know the yama sounds to be iron masses, those with semivowels like wooden masses; / but a semivowel devoid of a yama sound one should indicate as a woollen mass.