The Anglo-Saxon Chronicle records how the Vikings swore an oath to King Alfred on a holy ring.
Her hine be stæl se here into Wæham West Seaxna fyrde. ⁊ siððan wið þone here se cyning frið nam. ⁊ him þa gislas sealdon þe on þam here weorþuste wæron to þam cyninge. ⁊ him þa aðas sworon on þam halgan beage. þe hi ær nanre þeode don noldon þet hi hredliceof his rice foron.
And this year the army stole into Wareham, a fort of the West-Saxons. The king afterwards made peace with them; and they gave him as hostages those who were worthiest in the army; and swore with oaths on the holy bracelet, which they would not before to any nation, that they would readily go out of his kingdom.
Anglo-Saxon Chronicle anno 876 (actually 875)