No challenge as to the competency of any judge shall be received or allowed; but if it is plain that the judge is disqualified under the provisions of section 284 of this title, the party objecting to competency may, in writing, file with the judge his objection, stating the grounds therefor and the judge shall thereupon proceed with the trial or withdraw therefrom, in accordance with his determination of the question of his disqualification. His decision shall be reduced to writing and filed with the papers in the case, but no appeal or stay shall be allowed from, or by reason of, his decision in favor of his own competency until after final judgment in his court.