俱舍論疏 24.153

24.153

「論曰至已離故」，明諸無漏道唯未至定，能離自、下及上地染，自餘諸地唯離自、上地染。欲界無道，故依上未至斷。自餘諸無漏，唯在根本地中，非未至故。離下地染方得上地，由此上地不能斷下。

On the statement: "The Śāstra says: up to because it has already been abandoned": This clarifies that among all anāsrava paths, only the threshold concentration (anāgamya-samādhi) can abandon defilements of its own ground, lower grounds, and higher grounds; the remaining grounds only abandon defilements of their own and higher grounds. Since the desire realm has no path, one relies on the threshold above it to sever them. The remaining anāsrava paths exist only in the fundamental grounds (maulabhūmi) and not in the threshold; one only attains a higher ground after abandoning the defilements of the lower ground; hence a higher ground cannot sever a lower one.