成唯識論述記 7.80

7.80

述曰：尋、伺與悔、眠俱得相應，前二與自及與後二得相應義，行相不違故，然無四法一時並義。

The Commentary states: Investigation and examination can both associate with regret and torpor; the first two can associate with themselves and with the latter two, because their modes of activity (ākāra) are not mutually contrary. However, there is no sense in which all four dharmas can occur side by side at a single time.