《徐霞客游记·粤西游日记十九》
虽然未走到洞中，两头的源流全都见到了，可以不必麻烦再在黑暗中摸索。洞口右边的石崖，石痕丛聚繁多，全呈马蹄形，《西事饵》所说的 天马 ，料想就是此处了。
穷其西北，遂入阴洞后门，洞甚虚敞，分之则二，合之则一。右崖，石痕丛沓繁多，俱作马蹄形，《西事珥》所谓 天马 ，意即此矣。
Although I have not reached the cave, I can see the sources of the two streams, so I don't have to bother to grope in the dark anymore. There are many stone marks on the stone cliff to the right of the cave entrance, all in the shape of horseshoes. I guess this is the "Celestial Horse" mentioned in "Xi Shi'er".