大毘盧遮那經供養次第法疏 1.32

1.32

「十方無量世界中」以下，第六隨喜方便真言門，亦有誦真言。如實智自無有嫉，自無嫉智令無瞋嫉。至誠念誦此真智，令不異真實之智，故言隨喜方便法。

From "In the immeasurable worlds of the ten directions" onward is the sixth, the mantra gate of the upāya of rejoicing [in others' merits], which also has the recitation of a mantra. True wisdom is naturally free from jealousy, and wisdom naturally free from jealousy keeps one free from anger and jealousy. Reciting this true wisdom with utmost sincerity causes one not to differ from the wisdom of reality, and therefore it is called the method of the upāya of rejoicing.