首楞嚴義疏注經 5.166

5.166

我於向晦宴然安息在於靜室，清靜之室洗心之處，故名清齋。靜室聞香是有為相，即所觀境也。

I rested peacefully towards dusk in a quiet chamber; a quiet and clean chamber is a place where the mind is washed, hence it is called a 'pure retreat.' Smelling fragrance in a quiet chamber is a conditioned characteristic, which is precisely the objective realm under contemplation.