735 ILCS 5/2-1103: Affidavits.

(a) All affidavits presented to the court shall be filed with the clerk.

(b) If evidence is necessary concerning any fact which according to law and the practice of the court may now be supplied by affidavit, the court may, in its discretion, require the evidence to be presented, wholly or in part, by oral examination of the witnesses in open court upon notice to all parties not in default, or their attorneys. If the evidence is presented by oral examination, an adverse party shall have the right to cross-examination. This Section does not apply to applications for change of venue on grounds of prejudice.