CC Madhya 22.34

sakṛd eva prapanno yas
tavāsmīti ca yācate
abhayaṁ sarvadā tasmai
dadāmy etad vrataṁ mama
Synonyms: 
sakṛt — once only; eva — certainly; prapannaḥ — surrendered; yaḥ — anyone who; tava — Yours; asmi — I am; iti — thus; ca — also; yācate — prays; abhayam — fearlessness; sarvadā — always; tasmai — unto him; dadāmi — I give; etat — this; vratam — vow; mama — My.
Translation: 
“ ‘It is My vow that if one only once seriously surrenders unto Me, saying “My dear Lord, from this day I am Yours,” and prays to Me for courage, I shall immediately award courage to that person, and he will always remain safe from that time on.’
Purport: 

This verse from the Rāmāyaṇa (Yuddha-kāṇḍa 18.33) was spoken by Lord Rāmacandra.