CC Madhya 22.127

sarvathā śaraṇāpatti, kārtikādi-vrata
‘catuḥ-ṣaṣṭi aṅga’ ei parama-mahattva
Word for word: 
sarvathā — in all respects; śaraṇa-āpatti — surrender; kārtika-ādi-vrata — to observe special vows in the month of Kārttika; catuḥ-ṣaṣṭi aṅga — sixty-four parts; ei — this; parama-mahattva — very important items.
Translation: 
“(34) One should surrender to Kṛṣṇa in all respects. (35) One should observe particular vows like kārttika-vrata. These are some of the sixty-four important items of devotional service.