Tex. R. Civ. P. 252
If the ground of such application be the want of testimony, the party applying therefor shall make affidavit that such testimony is material, showing the materiality thereof, and that he has used due diligence to procure such testimony, stating such diligence, and the cause of failure, if known; that such testimony cannot be procured from any other source; and, it if be for the absence of a witness, he shall state the name and residence of the witness, and what he expects to prove by him; and also state that the continuance is not sought for delay only, but that justice may be done; provided that, on a first application for a continuance, it shall not be necessary to show that the absent testimony cannot be procured from any other source.The failure to obtain the deposition of any witness residing within 100 miles of the courthouse or the county in which the suit is pending shall not be regarded as want of diligence when diligence has been used to secure the personal attendance of such witness under the rules of law, unless by reason of age, infirmity or sickness, or official duty, the witness will be unable to attend the court, or unless such witness is about to leave, or has left, the State or county in which the suit is pending and will not probably be present at the trial.
Tex. R. Civ. P. 252