Mishkat al-Masabih #293
Purification
The Arabic includes the chain of narration (sanad) and the collector's commentary; the English translation shows the Prophet's words only.
وَعَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسلم: «مِفْتَاحُ الصَّلَاةِ الطُّهُورُ وَتَحْرِيمُهَا التَّكْبِيرُ وَتَحْلِيلُهَا التَّسْلِيمُ» . رَوَاهُ أَبُو دَاوُد وَالتِّرْمِذِيّ والدارمي
وَرَوَاهُ ابْنُ مَاجَهْ عَنْهُ وَعَنْ أَبِي سَعِيدٍ
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.”
Abu Dawud, Tirmidhi and Darimi transmitted it, and Ibn Majah transmitted it both from 'Ali and from Abu Sa'id.
Topics
About Mishkat al-Masabih
This hadith is #293 from Mishkat al-Masabih, in the Book of Purification.