Skandapurana 16.17.141

16.17.141

tāni te kathayāmyadya daśa sāmāni sundari..
huṃkāraḥ praṇavodgīthaḥ prastāvaśca catuṣṭayam .. 141 ..

I tell those ten Sāmans to you today, O beautiful woman: / the huṃkāra, the praṇava, the udgītha, and the prastāva make four;