Arthashastra
तीर्थ समवाये च आसां यथा विवाहं पूर्व ऊढां जीवत् पुत्रां वा पूर्वं गच्छेत् ॥
If many or all of them are at the same time in menses, he shall lie with that woman among them, whom he married earlier or who has a living son.
english translation
tIrtha samavAye ca AsAM yathA vivAhaM pUrva UDhAM jIvat putrAM vA pUrvaM gacchet ॥
hk transliteration by Sanscript