Vishnupurana 5.23.1

5.23.1

parāśara uvāca:
gārgyaṃ goṣṭhyāṃ dvijaṃ śyālaḥ ṣaṇḍa ity uktavān dvija
yadūnāṃ saṃnidhau sarve jahasur yādavās tataḥ //

PARÁŚARA.--Śyála having called Gárgya the Brahman, whilst at the cow-pens, impotent, in an assembly of the Yádavas, they all laughed; at which he was highly offended, and repaired to the shores of the western sea, where he engaged in arduous penance to obtain a son, who should be a terror to the tribe of Yadu. Propitiating Mahádeva, and living upon iron sand for twelve years, the deity at last was pleased with him, and gave him the desired boon. The king of the Yavanas, who was childless, became the friend of Gárgya; and the latter begot a son by his wife, who was as black as a bee, and was thence called Kálayavana. The Yavana king having placed his son, whose breast was as hard as the point of the thunderbolt, upon the throne, retired to the woods. Inflated with conceit of his prowess, Kálayavana demanded of Nárada who were the most mighty heroes on earth. To which the sage answered, "The Yádavas." Accordingly Kálayavana assembled many myriads of Mlechchhas and barbarians, and with a vast armament of elephants, cavalry, chariots, and foot, advanced impatiently against Mathurá and the Yádavas; wearying every day the animal that carried him, but insensible of fatigue himself.