Minister Vassakara was sent by Ajatashatru to the Buddha to seek his advice on attacking the Vajjis. The incident is mentioned in the Buddhist text, the Mahaparinibbana Sutta.

Explanation:

The Vajjis were a confederacy of eight clans in ancient India, who were known for their democratic governance and military strength. Ajatashatru, the king of Magadha, was envious of their power and wanted to conquer them. He sought the advice of his ministers on how to defeat the Vajjis.

One of his ministers, Vassakara, suggested that they attack the Vajjis, as they were weakened by internal conflicts. However, another minister, Sunidha, advised against it, stating that the Vajjis were a formidable enemy and that attacking them would be unwise.

Ajatashatru was indecisive and decided to seek the advice of the Buddha, who was residing nearby. He sent Vassakara to the Buddha with instructions to ask him whether attacking the Vajjis would be successful or not.

The Buddha, who was aware of the situation, used the opportunity to impart a lesson on the importance of unity and cooperation. He told Vassakara that the Vajjis were strong and prosperous because they were a united people who followed the Dhamma. He advised Ajatashatru to refrain from attacking the Vajjis and instead focus on building unity and harmony in his own kingdom.

Ajatashatru heeded the Buddha's advice and did not attack the Vajjis. The incident shows the reverence and respect that even powerful kings had for the Buddha and his teachings.