सिद्धं यत्सर्वभूतादि विश्वाधिष्ठानमव्ययम् ।यस्मिन्सिद्धाः समाविष्टास्तद्वै सिद्धासनं विदुः ॥ ११३ ॥
In plain words
What is eternally accomplished, the origin of every being, the ground the whole universe stands on, never wearing away — and the perfected ones are absorbed in it completely: that, and only that, the knowers call siddhāsana, the perfect seat.
Close to the Sanskrit
That which is [ever] accomplished, which is the origin of all beings, the substratum of the universe, imperishable — in which the perfected ones are wholly absorbed — that indeed they know as siddhāsana.