Incipiebant autem annum ab octavo Calendarum Januariarum die, ubi nunc natale Domini celebramus. Et ipsam noctem nunc nobis sacrosanctam, tunc gentili vocabulo Modranicht, id est, matrum noctem appellabant: ob causam et suspicamur ceremoniarum, quas in ea pervigiles agebant.
-Bede, De Temporum Ratione
... began the year on the 8th calends of January, when we celebrate the birth of the Lord. That very night, which we hold so sacred, they used to call by the heathen word Modranecht, that is, "mother's night", because (we suspect) of the ceremonies they enacted all that night.
-Bede, The Reckoning of Time
Bede writing in 725 states that the heathens marked their new year on the 8th calends of January, or the evening of the 24th of December. Bede additionally noted that Yule is marked by the winter solstice, or at least at the time of the turning back of the sun. During Bede's time Yule would have occurred between the 19th and 22nd of December and not as late as the 24th or 25th of December. We can therefore logically separate the feast of Yule from Mothers Night. In the year 725 the 24th of December was marked by the first full moon following Yule, (the winter solstice). We may therefore make an assumption that Yule occurs at the winter solstice and Mothers Night is marked by the first full moon following Yule
It seems that Bede's 'Mothers Night' or 'Night of The Mothers' is a continuation of the Germanic cult of 'Matres and Matronae' - a knowledge of which was still extant in Bede's eighth century Northumbria. The Matronae cults were seemingly highly localised and were a focus for worship which did not involve calling upon any 'higher Gods'. Mothers Night was observed with watchful rites, though what these privileges were that lasted all day was left unrecorded by the venerable monk.
Scholars have suggested that Mothers Night as well as being a sacrificial festival associated with the Matronae cult may also be connected to the Norse dísablót and disting. Additionally there may be further connections to be drawn from the Mothers venerated during Mothers Night and the Scandinavian dísir and Norns.