וְכֹל֩ אֲשֶׁ֨ר תִּשְׁכַּ֥ב עָלָ֛יו בְּנִדָּתָ֖הּ יִטְמָ֑א וְכֹ֛ל אֲשֶׁר־תֵּשֵׁ֥ב עָלָ֖יו יִטְמָֽא׃
And every thing that she lieth upon in her impurity shall be unclean; every thing also that she sitteth upon shall be unclean.
Read halakhic rulings (Jewish law) on Leviticus 15:20: and classical halakhic sources.