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)
عَنْ رَسُولِ اللهِ ﷺ قَالَ «مِفْتَاحُ الصَّلَاةِ الطُّهُورُ وَتَحْرِيمُهَا التَّكْبِيرُ وَتَحْلِيلُهَا التَّسْلِيمُ»