Muhammad bin al-Hanafiyyah (may Allah have mercy on him) narrates from Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "The key to prayer is purification; what makes things forbidden in it is the takbir (that is, once the opening takbir is said, everything that contradicts the prayer becomes forbidden); and what makes them lawful again is the salam (that is, once the salam is said, all those acts become permissible)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3970
Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "The key to prayer is ablution; what makes things forbidden in it is the takbir; and what makes them lawful is the salam."
Abu Umar al-Darir is alone in narrating it in this way, according to what Ibn Sa'id and many of the hadith masters claimed; however, Habban bin Hilal corroborated him in it from Hassan, so it is Hassan who is alone in narrating it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3971
Hadith Gradingمحدثین:حسن
Hadith Takhrij«حسن۔ رواه ابن ابي شيبة في للصنف 2307»
Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "The key to prayer is ablution; what makes things forbidden in it is the takbir; and what makes them lawful is the salam."
This is the preserved (mahfuz) version from Abu Sufyan Tarif al-Sa'di, and the hadith of Abu Sa'id revolves around him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3972
Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "The key to prayer is ablution, its tahrim (entry into its sanctity) is the takbir, and what makes things lawful again is turning with the salam; in every two rak'ahs there is a salam; and the prayer is not complete unless Surah al-Fatihah and something else besides it is recited."
Abu Abd al-Rahman (may Allah have mercy on him) says: I asked Abu Hanifah (may Allah have mercy on him): What is meant by "in every two rak'ahs there is a salam"? He said: By it the tashahhud is meant.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3973
Hadith Gradingمحدثین:صحيح لغيرهٖ
Hadith Takhrij«صحيح لغيرهٖ۔ وله شاهد رواه الطبراني في مسند الشامين 2/289»
Ata bin Abi Rabah (may Allah be pleased with him) narrates that when the Messenger of Allah (peace and blessings be upon him) sat at the end of his prayer, before the tashahhud he would turn his blessed face towards the people, and this was before the command of the salam was revealed.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3974