Why a + ablative?

Latin Learning Latin
1

Hello,
I have see the following sentence:

Servī tristēs senēsque auxilium sapientī ā vāte petent.

It is translated from this original:
The sad and old servants will seek aid of the wise soothsayer.

Now, my question is: why did they use “a” + ablative? Is it a mistake? Or what complement is it?
I would have used the genitive: vātis.
Any explanation?

Thank you.

2

peto

To beg, beseech, ask, request, desire, entreat (syn.: rogo, flagito, obsecro); constr with ab and abl. of pers.

3

Thank you.