Umm Sulaym, the mother of Anas bin Malik (may Allah be pleased with them both), narrates that the Messenger of Allah (peace and blessings be upon him) said: "When a woman dies and they intend to wash her," (he narrated the long hadith in full) and he said: "Then pack her lower part with cotton as much as you can. Then soak that cotton in perfume. Then take a long, clean cloth and tie it around her waist as a waistband is tied. Then knot it between her thighs and press her hips together. Then lay one end of the cloth from her waist down to her knees. This is what is meant by 'her lower part' (sulfah). Then perfume her and shroud her."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6701