四分比丘戒本疏 1.38

1.38

第五、媒嫁戒。和合生死，深失正念故也。語書使等，皆是犯限。凡得附書，須看持往，不看者吉罪，如律所說。

The fifth is the precept on acting as a go-between. This is because bringing together saṃsāra causes a profound loss of correct mindfulness. Words, letters, messengers, and the like are all within the bounds of transgression. Whenever one is entrusted with a letter, one must inspect it before carrying it; if one does not inspect it, it is a duṣkṛta offence, as stated in the Vinaya.