Skandapurana 1.3.3.167

1.3.3.167

tvaṃ gurustvaṃ mahāmaṃtro maṃtravedyo'si sarvadā..
tasmāttvadaparaṃ nānyattriṣu lokeṣu kiṃcana.. 5.167 ..

You are the guru, you are the great mantra, you are always to be known through mantra; / therefore, there is nothing else other than you in the three worlds.”