Pakiṇṇaka 15

The Buddha was staying at Sāvatthī. At that time, bhikkhunīs went to the women’s bathing place to wash their menstrual cloths. The women were upset and said: “These renunciates are staining the water red like this.” For this reason the bhikkhunīs went and informed … The Buddha said: “From now on, it’s no longer allowed to wash a menstrual cloth at the women’s bathing place. If (a bhikkhunī) washes one, she breaks a minor vinaya rule.” This is called the rule on washing menstrual cloth at the women’s place.