The Messenger of Allah ﷺ said: “The key to prayer is purification; entering it is takbeer and exiting it is tasleem.” (Using translation from Aḥmad 1006)  

قَالَ رَسُولُ اللَّهِ ﷺ «مِفْتَاحُ الصَّلَاةِ الطُّهُورُ وَتَحْرِيمُهَا التَّكْبِيرُ وَتَحْلِيلُهَا التَّسْلِيمُ»