It is mentioned in Sri Hari-bhakti-sudhodaya (13.2):
aksnoh phalam tvadrsa-darsanam hi
tanoh phalam tvadrsa-gatra-sangah
jihva-phalam tvadrsa-kirtanam hi
sudurlabha bhagavata hi loke
tanoh phalam tvadrsa-gatra-sangah
jihva-phalam tvadrsa-kirtanam hi
sudurlabha bhagavata hi loke
Devotees of Bhagavan are extremely rare in this world. Therefore the perfection of the eyes is to see them, the perfection of the body is to touch them and the perfection of the tongue is to glorify them.