Maitrāyaṇīya Āraṇyaka 5.4

5.4

nama̍ḥ śā̱ntātma̍ne tubhya̱ṃ namo̍ gu̱hyata̍māya ca
aci̍ntyāyāprame̱yāya̱ anā̍dini̱dhanā̍ya̱ ca

Reverence to you, whose self is peace, and reverence to the most secret one,
to the unthinkable, the immeasurable, and the one without beginning or end!'