瑜伽師地論略纂 9.20

9.20

論云解第二靜慮中言「所言定」者，謂已獲得加行究竟作意故。此與初靜慮異，彼名離生；此名定生。彼得初離欲界繫，名離生；此約先已得定故，故言定生。

Regarding the śāstra's explanation of the second dhyāna, which states: "The so-called concentration means having already obtained the manaskāra of culminating praxis": this differs from the first dhyāna. That one is called "born of separation," while this one is called "born of concentration." In that one, obtaining initial separation from the bonds of the desire realm is called "born of separation"; in this one, because one has previously already obtained concentration, it is called "born of concentration."