ततः सुषुप्तसंस्थानं स्थित्वा स्थित्वा विभुर्मनाक् ।सुषुप्ते स्थैर्यमासाद्य तुर्यरूपमुपाययौ
In plain words
Then, resting again and again, by slight degrees, in the condition of suṣupti, the all-pervading one, having attained steadiness there, arrived at the form of turya.