Ibn Jurayj (may Allah have mercy on him) says: I asked Ayyub (may Allah have mercy on him): What do the words 'ash'irnaha iyyahu' mean; is she to be girded with it as a waist-wrapper? He said: I do not think so. Ibn Sirin used to say: "She is wrapped in a cloth beneath the shift (dir')", and I think it means only that.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6772