Srimad Bhagavatam Canto 10, Chapter 20, Text 09

SB 10.20.9

srutva parjanya-ninadam
 mandukah sasrjur girah
tusnim sayanah prag yadvad
 brahmana niyamatyaye
The frogs, who had all along been lying silent, suddenly began croaking when they heard the rumbling of the rain clouds, in the same way that brahmana students, who perform their morning duties in silence begin reciting their lessons when called by their teacher.
Srila Prabhupada comments: “After the first rainfall, when there is a thundering sound in the clouds, all the frogs begin to croak, like students suddenly engaged in reading their studies. Students are generally supposed to rise early in the morning. They do not usually arise of their own accord, however, but only when there is a bell sounded in the temple or other spiritual institution. By the order of the spiritual master they immediately rise, and after finishing their morning duties they sit down to study the Vedas or chant Vedic mantras. Everyone is sleeping in the darkness of Kali-yuga, but when there is a great acarya, by his calling only everyone takes to the study of the Vedas to acquire actual knowledge.”
Srimad Bhagavatam Canto 10, Chapter 20, Text 08
Srimad Bhagavatam Canto 10, Chapter 20, Text 10