towel

Impurity on the bed

Q: If a towel was put on the bed and some semen after intercourse went on it which then transferred to the other bottom side of the towel which was touching the bed sheet then does that mean the bed sheet is also impure? This is because the wetness of the semen from the bottom side of the towel touching the bedsheets could've been transferred. Although when checked after few minutes the sheet was dry and and there were no stains. Should I have to wash the bed sheet?