首楞嚴義疏注經 8.559

8.559

鼓天池，嚥津液，固精華，歲久功著遂成潤德。言天行者，此非六欲，乃是世人謂靈仙居處名之為天，如張騫尋河源至崑崙，見天宮之類。或所行不交欲境，如天無異，故云天行。

Rousing the Heavenly Pool, swallowing saliva, and solidifying the vital essence, when the practice is applied for years, it finally accomplishes moistening virtue. As for 'heaven-roaming', this is not the six desire [heavens], but rather worldly people referring to the dwelling of divine immortals as 'heaven'—like Zhang Qian seeking the source of the Yellow River up to Kunlun and seeing the heavenly palace and the like. Or, their activities do not contact desire-objects, being no different from heaven, hence called heaven-roaming.