According to the traditional biography of Aśvaghoṣa 1, which was translated into Chinese by Kumārajīva, and preserved in that language, he was originally a wandering ascetic who was able to defeat all-comers in debate.
He set a challenge to the Buddhist monks that if none could meet with him in debate then they should stop beating the wood-block which signalled to the people to bring offerings to them. There was no one there to meet the challenge so they stopped beating the wood-block.
However, in the north there was an elder bhikṣu named Pārśva at the time, who saw that if he could convert this ascetic, it would be a great asset to the propagation of the Dharma, so he traveled from northern India, and had the wood-block sounded.
The ascetic came to ask why it had been sounded and though thinking the old monk would be unable to debate with him, he accepted his challenge, and after seven days the debate was held in front of the King, his Ministers, and many ascetics and brahmans. The loser agreed to become the disciple of the other.
They agreed that the elder Pārśva should speak first, and he said: “The world should be made peaceable, with a long-lived king, plentiful harvests, and joy throughout the land, with none of the myriad calamities”, to which the ascetic had no response and so was bound to become Pārśva’s disciple, and he was given full ordination as a bhikṣu.
Although he had to consent to this, he still wasn’t convinced of the elder’s virtues until he showed him he had mastered the Bases of Spiritual Power [r̥ddhipādāḥ], at which point he gained faith. Pārśva then taught him the 5 Faculties, the 5 Powers, the 7 Factors and the 8-fold Noble Path and he eventually mastered the teaching.
Later the central kingdom was besieged by the Kuṣāna King’s army, who demanded 300,00 gold pieces in tribute. The King could not pay so much as he had only 100,000. The Kuṣāna King therefore asked for the Buddha’s begging bowl, the converted monk and the 100,000 gold pieces for his tribute.
Although the King of the central kingdom was unhappy, the monk persuaded him it would be for the good of the propagation of the Dharma which would spread across the four continents if he went with the Kuṣāna King. He was therefore taken away.
The Kuṣāna’s King’s Ministers however, were unhappy, not thinking that the bhikṣu was priced correctly at 100,000 gold pieces. The King, who knew his worth, ordered that seven horses be starved for six days, then he made an assembly and had the bhikṣu preach the Dharma.
Even the horses, whose favourite food was placed in front of them, were entranced by the Teaching of the monk, and listened intently. Eveerybody was thereby convinced of his worth, and he then gained the name Aśvaghoṣa, Horse-Cry.
He traveled throughout northern India proclaiming the Dharma and guiding all through his wisdom and understanding, and he was held in great regard by the four-fold assembly, who knew him as The Sun of Merit and Virtue.