All vowels (svara) belong to Indra, all sibilants (ûshman) to Pragâpati, all consonants (sparsa) to Mrityu (death). If somebody should reprove him for his vowels, let him say, 'I went to Indra as my refuge (when pronouncing my vowels): he will answer thee.'

In plain words: The sounds of speech belong to different gods: vowels to Indra, hissing sounds like 's' to Prajāpati, and stop consonants to Mrityu, which means Death. If someone criticizes the singer's vowels, he should say he relied on Indra, and Indra will answer them.