Abu Sa'eed narrated that : Allah's Messenger said: "the key to Salat is the purification, its Tahrim is the Takbir, and its Tahlilis the Taslim, and there is no Salat for one who did not recite Al-Hamd and a Surah in the obligatory (prayer) or other prayers"
SahihSahihDaifBook 2 · Hadith 90