CC Madhya 19.156

yadi vaiṣṇava-aparādha uṭhe hātī mātā
upāḍe vā chiṇḍe, tāra śukhi’ yāya pātā
Word for word: 
yadi — if; vaiṣṇava-aparādha — an offense at the feet of a Vaiṣṇava; uṭhe — arises; hātī — an elephant; mātā — mad; upāḍe — uproots; — or; chiṇḍe — breaks; tāra — of the creeper; śukhi’ — shriveling up; yāya — goes; pātā — the leaf.
Translation: 
“If the devotee commits an offense at the feet of a Vaiṣṇava while cultivating the creeper of devotional service in the material world, his offense is compared to a mad elephant that uproots the creeper and breaks it. In this way the leaves of the creeper are dried up.
Purport: 

One’s devotional attitude increases in the association of a Vaiṣṇava:

tāṅdera caraṇa sevi bhakta-sane vāsa
janame janame haya, ei abhilāṣa

By his personal example, Narottama dāsa Ṭhākura stresses that a devotee must always remember to please his predecessor ācārya. The Gosvāmīs are represented by one’s spiritual master. One cannot be an ācārya (spiritual master) without following strictly in the disciplic succession of the ācāryas. One who is actually serious about advancing in devotional service should desire only to satisfy the previous ācāryas. Ei chaya gosāñi yāra, mui tāra dāsa. One should always think of oneself as a servant of the servant of the ācāryas, and thinking this, one should live in the society of Vaiṣṇavas. However, if one thinks that he has become very mature and can live separate from the association of Vaiṣṇavas and thus gives up all the regulative principles due to offending a Vaiṣṇava, one’s position becomes very dangerous. Offenses against the holy name are explained in Ādi-līlā, chapter eight, verse 24. Giving up the regulative principles and living according to one’s whims is compared to a mad elephant, which by force uproots the bhakti-latā and breaks it to pieces. In this way the bhakti-latā shrivels up. Such an offense is especially created when one disobeys the instructions of the spiritual master. This is called guru-avajñā. The devotee must therefore be very careful not to commit offenses against the spiritual master by disobeying his instructions. As soon as one is deviated from the instructions of the spiritual master, the uprooting of the bhakti-latā begins, and gradually all the leaves dry up.