CC Madhya 22.48

naivopayanty apacitiṁ kavayas taveśa
brahmāyuṣāpi kṛtam ṛddha-mudaḥ smarantaḥ
yo ’ntar bahis tanu-bhṛtām aśubhaṁ vidhunvann
ācārya-caittya-vapuṣā sva-gatiṁ vyanakti
Synonyms: 
na eva — not at all; upayanti — are able to express; apacitim — their gratitude; kavayaḥ — learned devotees; tava — Your; īśa — O Lord; brahma-āyuṣā — with a lifetime equal to Lord Brahmā’s; api — in spite of; kṛtam — magnanimous work; ṛddha — increased; mudaḥ — joy; smarantaḥ — remembering; yaḥ — who; antaḥ — within; bahiḥ — outside; tanu-bhṛtām — of those who are embodied; aśubham — misfortune; vidhunvan — dissipating; ācārya — of the spiritual master; caittya — of the Supersoul; vapuṣā — by the forms; sva — own; gatim — path; vyanakti — shows.
Translation: 
“ ‘O my Lord! Transcendental poets and experts in spiritual science could not fully express their indebtedness to You, even if they were endowed with the prolonged lifetime of Brahmā, for You appear in two features — externally as the ācārya and internally as the Supersoul — to deliver the embodied living being by directing him how to come to You.’
Purport: 

This is a verse from Śrīmad-Bhāgavatam (11.29.6). It was spoken by Uddhava after he had been instructed in yoga by Śrī Kṛṣṇa.