This is a leniency for which the one who acts upon it will be rewarded, and the one who rejects it will be blameworthy. The original ruling as mentioned by (the narrator's) father in his letter states: "Pray in silk (khazz) as long as it is not mixed with rabbit fur." He also stated: "Do not pray in brocade, pure silk, or embroidered silk, except if it is a garment with silk warp and cotton or linen weft."
Commentary #9