This quote is found in 8th Patala of Karana Agama:
देवदेव जगन्नाथ सर्वानुग्रहतत्पर।
वेदाधिकारिणां सम्यगनुष्टेयं प्रकाशितम्।
स्रीमुख्याः केन विधिना कृतार्थाः स्युर्निबोध मे।।
Oh The Gods of Gods, the Lord of World, You are ready to grace all. This well-mannered method is connected with the hymns of Vedas. Its practice of the learned of Vedas has been made known in well-manner. Reveal to me by which method women etc. achieve their object of desire.
महादेवि प्रवक्ष्यामि तान्त्रिकं पूजनक्रमम्।
अनुष्ठितेन येन स्यु: सर्वे सर्वार्थभाजना:।।
विद्यासु श्रुतिरुत्कृष्टा रुद्रैकादशिनी श्रुतौ।
तत्र पञ्चाक्षरस्तत्र शिव इत्यक्षरदूयम् ।।
Oh, Mahadevi! I would reveal a method of Tantrik worship of which performance all and the complete Arthas achieved. Shrutis/Vedas are the best and excellent among all Vidyas (sources of knowledge); In Shrutis also Sri Rudram hymn is the Supreme, in Sri Rudram also Panchakshara is Supreme and in the Panchakshara also the two letters 'Shiva' is Supreme.