Nafi' narrates that Sayyiduna Ibn Umar (may Allah be pleased with them both) saw me praying in a single garment and said: "Did I not clothe you?" I said: "Of course, you certainly did." He said: "If I were to send you somewhere in this state, would you go?" I said: "No." He said: "Then Allah Almighty is the most deserving that one should adorn oneself for Him." Then he said that the Messenger of Allah (peace and blessings be upon him) said: "When one of you prays in a single garment, let him tie it around his waist or flank, and do not wrap the sheet around yourselves the way the Jews do, so that even the hands cannot come out."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3272