Sayyiduna Ibn Umar (may Allah be pleased with them) narrates from the Noble Prophet (peace and blessings be upon him) that he (peace be upon him) said: "Make your last prayer at night the Witr."
Hadith Referenceصحيح ابن خزيمه / جماع أبواب ذكر الوتر وما فيه من السنن / 1082