Pakiṇṇaka 16

The Buddha was staying at Sāvatthī. At that time, the World-honored One had laid down the precept that it’s not allowed to wash a menstrual cloth at the women’s bathing place. So the bhikkhunīs went to the men’s bathing place to wash it. … “If a bhikkhunī goes to the men’s bathing place to wash one, she breaks a minor vinaya rule.” This is called the rule on the men’s place.