俱舍論疏 7.93

7.93

「論曰至同類因義」，釋第一句，明四大於異類大具其二因，若自類大唯有一因謂同類因，水望於水非俱有因故。

The treatise says: "...the meaning of similar cause." This explains the first line, clarifying that the four great elements possess two causes with respect to different kinds of great elements; but with respect to the same kind of great element, there is only one cause, namely the similar cause, because water with respect to water is not a coexistent cause.