首楞嚴義疏注經 6.259

6.259

火頭金剛觀多婬心成智慧火，身心煖觸，無礙流通，生大寶焰。今謂此由多婬生厭離故，觀成性火。此即厭求之心豈稱圓照？非是真實離念之門，初機不合，故須揀也。

The Fire-Head Vajra (Ucchuṣma) contemplated his lustful mind as turning into the fire of wisdom; his body and mind were touched by warmth, circulating without hindrance and generating great treasure flames. Here it means: because this arises from revulsion toward excessive lust, he contemplated the fire of nature. Since this is a mind of revulsion and pursuit, how could it be called perfect illumination? It is not a gate of true detachment from thought, and does not suit initial capacities; therefore it must be selected out.