SB 6.1.37

śrī-śuka uvāca
ity ukte yamadūtais te
 vāsudevokta-kāriṇaḥ
tān pratyūcuḥ prahasyedaṁ
 megha-nirhrādayā girā
Word for word: 
śrī-śukaḥ uvāca — Śrī Śukadeva Gosvāmī said; iti — thus; ukte — being addressed; yamadūtaiḥ — by the messengers of Yamarāja; te — they; vāsudeva-ukta-kāriṇaḥ — who are always ready to execute the orders of Lord Vāsudeva (being personal associates of Lord Viṣṇu who have obtained the liberation of sālokya); tān — unto them; pratyūcuḥ — replied; prahasya — smiling; idam — this; megha-nirhrādayā — resounding like a rumbling cloud; girā — with voices.
Translation: 
Śukadeva Gosvāmī continued: Being thus addressed by the messengers of Yamarāja, the servants of Vāsudeva smiled and spoke the following words in voices as deep as the sound of rumbling clouds.
Purport: 

The Yamadūtas were surprised to see that the Viṣṇudūtas, although polite, were hindering the rule of Yamarāja. Similarly, the Viṣṇudūtas were also surprised that the Yamadūtas, although claiming to be servants of Yamarāja, the supreme judge of religious principles, were unaware of the principles of religious action. Thus the Viṣṇudūtas smiled, thinking, “What is this nonsense they are speaking? If they are actually servants of Yamarāja they should know that Ajāmila is not a suitable candidate for them to carry off.”