Sayyiduna Samurah (may Allah be pleased with him) said: the Messenger of Allah (peace and blessings be upon him) forbade that any of us should cut a thing, or a strap, between his two fingers with two marks: the mark of cutting, and that which is pressed in by the hand.
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6919