CC Antya 2.165

śuni’ prabhu hāsi’ kahe suprasanna citta
‘prakṛti darśana kaile ei prāyaścitta’
Word for word: 
śuni’ — hearing; prabhu — Śrī Caitanya Mahāprabhu; hāsi’ — smiling; kahe — replied; su-prasanna citta — being in a happy mood; prakṛti darśana kaile — if someone sees women with a sensual propensity; ei prāyaścitta — this is the atonement.
Translation: 
When Śrī Caitanya Mahāprabhu heard these details, He smiled in a pleased mood and said, “If with sensual intentions one looks at women, this is the only process of atonement.”