CC Madhya 20.249

avatārā hy asaṅkhyeyā
hareḥ sattva-nidher dvijāḥ
yathā ’vidāsinaḥ kulyāḥ
sarasaḥ syuḥ sahasraśaḥ
Word for word: 
avatārāḥ — all the incarnations; hi — certainly; asaṅkhyeyāḥ — beyond counting; hareḥ — from the Supreme Personality of Godhead; sattva-nidheḥ — who is the reservoir of spiritual energy; dvijāḥ — O brāhmaṇas; yathā — as; avidāsinaḥ — containing a great reservoir of water; kulyāḥ — small rivulets; sarasaḥ — from a lake; syuḥ — must be; sahasraśaḥ — by hundreds and thousands of times.
Translation: 
“ ‘O learned brāhmaṇas, just as hundreds and thousands of small rivulets issue from great reservoirs of water, innumerable incarnations flow from Śrī Hari, the Supreme Personality of Godhead and the reservoir of all power.’
Purport: 

This verse is quoted from Śrīmad-Bhāgavatam (1.3.26).