Baker v. State, 519 S.W.2d 437 (Tex.Crim.App.  1975).

Tennery v. State, 680 S.W.2d 629 (Tex.App.-Corpus Christi 1984, pet. ref’d).

Burden of proof is on defendant to show by sworn affidavit plus testimony (from some source) that he is eligible for probation.