One of the Wikipedia sources quotes the Chinese expert as saying he thinks the motif came from Central Asia, East to China, and represent peace and tranquility.

> Guan Youhui, a retired researcher from the Dunhuang Academy, spent fifty years studying the decorative patterns in the Mogao Caves. He believes the three-hares image came to Dunhuang indirectly from the West (Central Asia) by way of central China...

Since those instances were created at around 300-500 and later, seems like the very earliest instances of the motif came from the center of the known instances, which would be the eastern Mediterranean area. That also predates Islam and Buddhism.