Teyt 2611 Sāryabhauma Bhattācārya Offers Prasāda to the Lord
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In this conversation between Mārkaṇḍeya and Bhagīratha, it is said: “My dear King, if one derides an exalted devotee, he loses the results of his pious activities, his opulence, his reputation and his sons. Vaiṣṇavas are all great souls. Whoever blasphemes them falls down to the hell known as Mahāraurava. He is also accompanied by his forefathers. Whoever kills or blasphemes a Vaiṣṇava and whoever is envious of a Vaiṣṇava or angry with him, or whoever does not offer him obeisances or feel ioy upon seeing a Vaiṣṇava, certainly falls into a hellish condition.”
The  Hari-bhakti-vilāsa  (10.314) also gives the following quotation from  Dvārakā-māhātmya :
kara-patraiś ca phālyante sutīvrair yama-śāsanaiḥ nindāṁ kurvanti ye pāpā vaiṣnavānāṁ maḥātmanām
In a conversation between Prahlāda Mahārāja and Bali Mahārāja, it is said, “Those sinful people who blaspheme Vaiṣṇavas, who are all great souls, are subjected very severely to the punishment offered by Yamarāja.”
In the  Bhakti-sandarbha  (313) there is a statement concerning the blaspheming of Lord Viṣṇu.
ye nindanti hrșikeśaṁ tad-bhaktaṁ puṇya-rūpiṇam śata-janmārjitaṁ puṇyaṁ teṣāṁ naśyati niścitaṁ
te pacyante mahā-ghore kumbhīpāke bhayānake bhakṣitāḥ kīṭa-saṅghena yāvac candra-divākarau śrī-viṣṇor avamānanād gurutaraṁ śrī-vaiṣṇavollaṅghanam
tadīya-dūṣaka-janān 
        na paśyet puruṣādhamān 
    taiḥ sārdharṅ vañcaka-janaiḥ 
        saha-vāsarṅ na kārayet
“One who criticizes Lord Vişñu and His devotees loses all the benefits accrued in a hundred pious births. Such a person rots in the Kumbhīpāka hell and is bitten by worms as long as the sun and moon exist. One should therefore not even see the face of a person who blasphemes Lord Vişñu and His devotees. Never try to associate with such persons.”