SB 6.3.4
yamaduta ucuh
kati santiha sastaro
jiva-lokasya vai prabho
trai-vidhyam kurvatah karma
phalabhivyakti-hetavah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The Yamadutas said: Our dear lord, how many controllers or rulers are there in this material world? How many causes are responsible for manifesting the various results of activities performed under the three modes of material nature [sattva-guna, rajo-guna and tamo-guna]?
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Srila Visvanatha Cakravarti Thakura says that the Yamadutas, the order carriers of Yamaraja, were so disappointed that they asked their master, almost in great anger, whether there were many masters other than him. Furthermore, because the Yamadutas had been defeated and their master could not protect them, they were inclined to say that there was no need to serve such a master. If a servant cannot carry out the orders of his master without being defeated, what is the use of serving such a powerless master?