瑜伽論記 2.60

2.60

第二靜慮受定生喜樂者，定謂已轉依者，心住一境，即前得定，生者，謂從定所生，喜如前，非如初定創初得離，故言定生，初定之先未有定，故但言離生，不言定生。

Regarding 'the second dhyāna experiences joy and pleasure born of concentration': 'concentration' refers to the one who has transformed the basis having the mind abide on a single object, namely the concentration obtained previously; 'born' refers to being produced from concentration; 'joy' is as before; it is not like the first dhyāna where one newly attains detachment for the very first time, hence it is called 'born of concentration'; prior to the first dhyāna there is not yet concentration, so it is only called 'born of detachment' and not 'born of concentration.'