Srimad-Bhagavatam: Canto 10 - Chapter 1 - Verse 4

Sanskrit:

अक्षौहिणीभिर्विंशत्या तिसृभिश्चापि संवृत: ।यदुराजधानीं मथुरां न्यरुधत् सर्वतोदिशम् ॥ ४ ॥

ITRANS:

akṣauhiṇībhir viṁśatyātisṛbhiś cāpi saṁvṛtaḥyadu-rājadhānīṁ mathurāṁnyarudhat sarvato diśam

Translation:

With a force of twenty-three akṣauhiṇī divisions, he laid siege to the Yadu capital, Mathurā, on all sides.

Purport:

The numbers involved in an akṣauhiṇī division are given in the word meanings. An akṣauhiṇī was a standard fighting force in ancient times.