It may have appeared in other texts as well, but it's definitely in the Bhagavata Purana; the very first line, in fact!
ॐ नमो भगवते वासुदेवाय॥
जन्माद्यस्य यतोऽन्वयादितरतश्चार्थेष्वभिज्ञः स्वराट् तेने ब्रह्म हृदा य आदिकवये मुह्यन्ति यत्सूरयः।
तेजोवारिमृदां यथा विनिमयो यत्र त्रिसर्गोऽमृषा धाम्ना स्वेन सदा निरस्तकुहकं सत्यं परं धीमहि॥१॥
Om̐ namo bhagavate vāsudevāya||
Janmādyasya yato'nvayāditarataścārtheṣvabhijñaḥ svarāṭ tene brahma hṛdā ya ādikavaye muhyanti yatsūrayaḥ|
Tejovārimṛdāṁ yathā vinimayo yatra trisargo'mṛṣā dhāmnā svena sadā nirastakuhakaṁ satyaṁ paraṁ dhīmahi ||1||
So I guess the verse number would be 1.1.1.
And the translation is also in the link above, though there's a more extended analysis here.
The sloka itself is known as the Dvadasaksari mantra, as @অনু notes in a comment, and Wisdomlib shows that the mantra itself is referenced in the Parama Samhita, as well as some other texts, including the Garuda Purana.