Srimad Bhagavatam Canto 10, Chapter 50, Text 44

SB 10.50.44

rurodha mathuram etya
 tisrbhir mleccha-kotibhih
nr-loke capratidvandvo
 vrsnin srutvatma-sammitan
Arriving at Mathura, this Yavana laid siege to the city with thirty million barbarian soldiers. He had never found a human rival worth fighting, but he had heard that the Vrsnis were his equals.
Srila Visvanatha Cakravarti quotes from the Visnu Purana concerning the history of Kalayavana: “Once, Gargya was ridiculed by his brother-in-law as a eunuch, and when the Yadavas heard this they laughed heartily. Infuriated by their laughter, Gargya set out for the south, thinking, ‘May I have a son who will bring terror to the Yadavas.’ He worshiped Lord Mahadeva, eating powdered iron, and after twelve years obtained his desired benediction. Elated, he returned home.
“Later, when the childless King of the Yavanas requested a son from him, Gargya begot in the Yavana’s wife a son, Kalayavana. Kalayavana possessed the fury of Lord Siva in his aspect as Mahakala. Once, Kalayavana asked Narada, ‘Who are now the strongest kings on earth?’ Narada replied that the Yadus were. Thus sent by Narada, Kalayavana appeared at Mathura.”
Srimad Bhagavatam Canto 10, Chapter 50, Text 43
Srimad Bhagavatam Canto 10, Chapter 50, Text 45