The Prophet ﷺ said, "The key to prayer is purification, its sanctification is the takbir, and its conclusion is the taslim."
حدثنا سويد بن سعيد حدثنا علي بن مسهر عن أبي سفيان طريف السعدي ح و حدثنا أبو كريب محمد بن العلاء حدثنا أبو معاوية عن أبي سفيان السعدي عن أبي نضرة
عن النبي ﷺ قال مفتاح الصلاة الطهور وتحريمها التكبير وتحليلها التسليم
[Hasan]: Tirmidhi narrated it, in the Book of Prayer, Chapter on What Has Been Said Regarding What Makes Prayer Forbidden and What Makes It Permissible, hadith 238, from the hadith of Abu Sufyan, through him, and he graded it hasan. See the previous hadith, for it serves as a corroborating witness for it.