It is narrated from Sayyiduna Ammar bin Yasir (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said regarding tayammum: "One strike is for the face and both hands."
Hadith Referenceصحيح ابن خزيمه / جماع أبواب التيمم عند الإعواز من الماء فى السفر، / 266