Which preposition to use with predicants

in Occurrences 1%

On this the new pope sent messengers to the Polos to call them back, or to delay their departure from Armenia until he might prepare other letters for them, to present to the khan in his name, and to inform them, that he meant to join two friars predicants in commission with them, Nicolo of Vicenza and Guelmo of Tripoli, men of learning and discretion.

Which preposition to use with  predicants