俱舍論疏 28.193

28.193

論「第二靜慮至并自地二」，明第二靜慮生八，識處生九，第三定、第四定、空處此三地皆生十，謂上、下各二地，并自地有五，五各二故總為十也。

The passage of the śāstra from 'The second dhyāna...' down to '...together with two of its own stage' explains that the second dhyāna gives rise to eight, the Sphere of Consciousness gives rise to nine, and the third dhyāna, fourth dhyāna, and Sphere of Empty Space—these three stages—each give rise to ten; that is, two stages above and two below, plus its own stage, makes five, and with two each for the five, the total is ten.