妙法蓮華經玄贊 2.6

2.6

There are four kinds of non-retrogression: first, non-retrogression of faith: the sixth of the ten faiths is called the non-retrogressing mind, because thereafter one does not retrogress to generate wrong views. Second, non-retrogression of stage: the seventh of the ten abidings is called the non-retrogressing stage, because thereafter one does not retrogress into the two vehicles. Third, non-retrogression of realization: from the first stage onward is called non-retrogression, because the dharmas realized are not lost. Fourth, non-retrogression of practice: from the eighth stage onward is called the non-retrogressing stage, because one is capable of cultivating both conditioned and unconditioned dharmas. Now, these bodhisattvas are all at or above the eighth stage, so the text says that they are non-retrogressing with respect to unsurpassed right and equal awakening because they are certain to realize it; thus "not retrogressing" (butui) does not merely mean "not turning back" (buzhuan).