وَعَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «مِفْتَاحُ الصَّلَاةِ الطُّهُورُ وَتَحْرِيمُهَا التَّكْبِيرُ وَتَحْلِيلُهَا التَّسْلِيمُ»
He also reported God’s messenger as saying, “The key of prayer is purification, saying ‘God is most great’ makes it a sacred state, and the salutation brings the sacred state to an end.”
Mishkat al-Masabih 294, Book 4, Purification, Hadith 30. 1 min read