Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV:
The Canons of the Council in Trullo; Often Called The Quinisext Council.: Canon XXIII

Canon XXIII.

That no one, whether bishop, presbyter, or deacon, when giving the immaculate Communion, shall exact from him who communicates fees of any kind.  For grace is not to be sold, nor do we give the sanctification of the Holy Spirit for money; but to those who are worthy of the gift it is to be communicated in all simplicity.  But if any of those enrolled among the clergy make demands on those he communicates let him be deposed, as an imitator of the error and wickedness of Simon.

Notes.

Ancient Epitome of Canon XXIII.

Whoever shall demand an obolus or anything else for giving the spotless communion shall be deposed.

This canon is found in the Corpus Juris Canonici, Gratian’s Decretum, Pars. II., Causa I., Quæst. I., can. 100, attributed to the VI. Synod.  Ivo reads, “From the Sixth Synod, III. Constantinople.”