Sahih Bukhari Volume 001, Book 008, Hadith Number 361.
Narated By Abu Huraira : A man stood up and asked the Prophet about praying in a single garment. The Prophet said, "Has every one of you two garments?" A man put a similar question to 'Umar on which he replied, "When Allah makes you wealthier then you should clothe yourself properly during prayers. Otherwise one can pray with an Izar and a Rida' (a sheet covering the upper part of the body.) Izar and a shirt, Izar and a Qaba', trousers and a Rida, trousers and a shirt or trousers and a Qaba', Tubban and a Qaba' or Tubban and a shirt." (The narrator added, "I think that he also said a Tubban and a Rida.")