大乘義章 11.69

11.69

行時別者，如《涅槃》說，以行分別故應立四。何者行別？修慈之時不得修餘，餘時亦爾，是為行別。以是別故，建立四種（此五門竟）。

As for the difference in the time of practice: as the Nirvāṇa [Sūtra] says, because of the distinction in practice, four should be established. What is the distinction in practice? At the time of cultivating loving-kindness, one cannot cultivate the others; the other times are also like this. This is the distinction in practice. Because of this difference, four kinds are established (this completes the fifth section).