Rule 137, Rules of Court
Sec. 1. Disqualification of judges. – No judge or judicial officer shall sit in any case in which he, or his wife or child, is pecuniarily interested as heir, legatee, creditor or otherwise, or in which he is related to either party within the sixth degree of consanguinity or affinity, or to counsel within the fourth degree, computed according to the rules of the civil law, or in which he has been executor, administrator, guardian, trustee or counsel, or in which he has presided in any inferior court when his ruling or decision is the subject of review, without the written consent of all parties in interest, signed by them and entered upon the record.
A judge may, in the exercise of his sound discretion, disqualify himself from sitting in a case, for just or valid reasons other than those mentioned above.