Baring-Gould’s sources: Anglican Martyrologies. Authorities:—Bede, lib. iii. c. 21, Ingulf, and William of Malmesbury.

An obstinate tradition found in the ancient English Chronicles asserts that two daughters of the savage old heathen Penda, king of Mercia [the Anglo-Saxon kingdom of the English Midlands], Kyneburga and Kyneswitha, both gave up the thought of marriage to consecrate themselves to God. The eldest, who was married to Alcfrid, the eldest son of king Oswy of Northumbria [the Anglo-Saxon kingdom of northern England and south-east Scotland], is said to have left him with his consent, after having lived with him some years in virginal continence, to end her life in the cloister. The youngest, sought in marriage by Offa, king of the East Saxons, used her connection with him only to persuade the young prince to embrace the monastic life as she herself desired to do. But it has been proved that the two daughters of the bloody Penda contributed with their brothers to the establishment of the great abbey of Medehampstede, or Peterborough, that their names appear in the list of the national assembly which sanctioned this foundation, and that it was not till after, that they retired to lead a religious life at Dermundcaster, now Caister, near Peterborough, on the confines of Huntingdon and Northampton. There Kyneburga became the abbess of a community of nuns, when she was shortly joined by her sister Kyneswitha, and a kinswoman Tibba.

After their death, they were buried at Peterborough. When the Danes [Viking raiders from Scandinavia] wasted England, their bodies were carried to Thorney, but were brought back again in the days of king Henry I.

Camden, in his account of Rutland, informs us that S. Tibba was held in particular veneration at Ryall on the Wash.