四分比丘戒本疏 2.21

2.21

第十三、增好毛作臥具戒。舊人名白毛臥具戒。今詳律文，增牻不犯，餘增皆犯，不局白毛也。謂縱增黑，不犯前戒，以其前戒純中制故。戒文應言二分黑、第三分白、第四分牻，義即自顯。且如四斤以作臥具，二斤純黑、一斤白、一斤牻是也。餘可准知。

Thirteenth: the precept concerning adding fine wool to make a rug. Ancients called it the precept of rugs with white wool. In my present examination of the Vinaya text, adding mixed-colour wool incurs no offence, while adding other wools incurs an offence; it is not restricted to white wool. That is to say, even if one adds black, it does not violate the previous precept, because the previous precept was instituted against pure [black wool]. The precept text ought to say two parts black, a third part white, and a fourth part mixed-colour; then the meaning becomes self-evident. For instance, if four catties are used to make a rug: two catties of pure black, one catty of white, and one catty of mixed-colour. The rest can be understood by analogy.