肇論新疏 3.293

3.293

無為即乘也。乘即無為也。此非我異無為，以未盡無為，故有三耳。

The unconditioned is identical to the vehicle; the vehicle is identical to the unconditioned. This is not that the self is different from the unconditioned; it is because they have not exhausted the unconditioned that there are three.