Brahma Sutras 3.10

अक्षरमम्बरान्तधृतेः ॥

aksharam ambaranta-dhriteh

The Imperishable is Brahman, because it is described as the support up to ether.

"अक्षर" (अविनाशी) [ब्रह्म है] क्योंकि [वह] आकाश-पर्यन्त [सबका] धारण करता है ॥