Romans 8.26f. has no parallel in the NT. A. J. M. Wedderburn writes,
Today it is still puzzling, troublesome, divisive; for some it is the essence of the Christian faith, to others it is incomprehensible and repellent.
This statement sums up adequately the position of most NT scholars on Rom. 8.26f. Its strangeness derives from three basic ideas. First, this is the only passage in which it is asserted that the Christian does not know how to pray as he ought. This is an exception to what is otherwise said of prayer in the NT. Second, this is the only passage in biblical writings where the Holy Spirit is described explicitly as an intercessor. Third, the passage appears disjointed from its context. The guiding thought in vv. 18–25 is suffering but in v. 26, Paul talks about prayer. Can these themes be related in a single unit?