What is the biblical basis for requiring that a pastor/preacher/teacher/etc be paid for their ministry?

What is the biblical basis for requiring a minister to be paid for their work? Put another way, what is the biblical basis for supporting the notion of a solely-vocational pastor? --- Note - I am ***NOT*** looking for a biblical basis that paying a minister *anything* is OK: there are myriad passages that could be turned to for that. This is exclusively about a *mandate* for such recompense.