Śaiśirīya Śikṣā 106

106

prathamottamavargīye vargyāntyaissaha saṃgate
nāsikyaṃ gurumuccāryaṃ yamasthānagataṃ vadet

When a first or last class-consonant is conjoined with the end-consonants of classes, / one should pronounce a heavy nasal, stating it to have reached the place of a yama.