Chapter IX · Śloka 31
क्षिप्रं भवति धर्मात्मा शश्वच्छान्तिं निगच्छति ।
कौन्तेय प्रतिजानीहि न मे भक्तः प्रणश्यति ॥
kṣipraṃ bhavati dharmātmā śaśvac chāntiṃ nigacchati |
kaunteya pratijānīhi na me bhaktaḥ praṇaśyati ||
He quickly becomes righteous and attains lasting peace. O son of Kuntī, declare it boldly: My devotee is never destroyed.
Transformation is swift once the orientation is correct. Kṛṣṇa asks Arjuna to proclaim this as a universal guarantee: no sincere devotee is ever lost. The verb pratijānīhi (declare, take as a vow) makes Arjuna himself a witness to this promise.