The Messenger of Allah ﷺ said, "The key to prayer is purification, its sanctification is the takbir, and its conclusion is the taslim. There is no prayer for one who does not recite al-Fatihah and a surah, whether in an obligatory prayer or otherwise."
حدثنا سفيان بن وكيع حدثنا محمد بن الفضيل عن أبي سفيان طريف السعدي عن أبي نضرة
قال رسول الله ﷺ مفتاح الصلاة الطهور وتحريمها التكبير وتحليلها التسليم ولا صلاة لمن لم يقرأ بالحمد وسورة في فريضة أو غيرها
[Its chain is daif] Ibn Majah also narrated it in "The Book of Purification," chapter "The key to prayer is purification," hadith no. 276, through the hadith of Abu Sufyan Tarif Saadi, with the same wording. Saadi is daif, as stated in Taqrib and elsewhere. However, the portion of the hadith from "the key" up to "and its exit is the closing salutation" is sahih, as mentioned previously at no. 3.On this subject there is also a hadith from Ali [mentioned previously at no. 3] and from Ayesha [Muslim, no. 498, which includes the opening and the closing salutation].The statement of Ibn Mahdi is sahih from him.