Hiranyakeshigrihyasutra 2.1.4.10

2.1.4.10

imaṃ me varuṇa \ tattvā yāmi \ tvaṃ no agne \ sa tvaṃ no agne \ tvamagne ayāsi \ prajāpate \ yadasya karmaṇotyarīricam \ iti ca \ atraike jayābhyātānānrāṣṭrabhṛta ityupajuhvati yathā purastāt \ brāhmaṇānannena pariviṣya puṇyāhaṃ svastyayanamṛddhimiti vācayitvā putrasya nāma dadhyāddvyakṣaraṃ caturakṣaraṃ vā ghoṣavadādyantarantasthaṃ dīrghābhiniṣṭhānāntaṃ yatra vā svityupasargaḥ syāt \ taddhi pratiṣṭhitamiti vijñāyate \10\

'This, O Varuna' (&c.; see I, chap. 27, Sûtra 2, down to): 'Hail! Good luck!' Then let him give a name to the child, of two syllables or of four syllables, beginning with a sonant, with a semi-vowel in it, with a long vowel (or) the Visarga at its end, or a name that contains the particle su, for such a name has a firm foundation; thus it is understood.