Srimad-Bhagavatam: Canto 10 - Chapter 1 - Verse 19
Sanskrit:
एतेषां पुत्रपौत्राश्च बभूवु: कोटिशो नृप ।मातर: कृष्णजातीनां सहस्राणि च षोडश ॥ १९ ॥
ITRANS:
eteṣāṁ putra-pautrāś cababhūvuḥ koṭiśo nṛpamātaraḥ kṛṣṇa-jātīnāṁsahasrāṇi ca ṣoḍaśa
Translation:
My dear King, the sons and grandsons of Lord Kṛṣṇa’s children numbered in the tens of millions. Sixteen thousand mothers gave rise to this dynasty.