(a) It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him): The Prophet (peace and blessings be upon him) taught me the tashahhud; then he mentioned the complete hadith.
(b) Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) says: When you have finished your prayer, then if you wish, remain seated there, and if you wish, give the salam.
(c) The Shaykh (may Allah have mercy on him) says: This phrase, 'fa-idha faraghta min salatik' (so when you have finished your prayer), if it is preserved, is closer to the narration that has reached us from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) about completing the prayer with the salam, and also to what we shall soon narrate from the Prophet (peace and blessings be upon him) about the salam. It is as though his (may Allah be pleased with him) intent was to oppose the one who holds that it is not permissible for the follower to turn away, after finishing the prayer, before the imam turns away. And even if the first wording is established from the Prophet (peace and blessings be upon him), it will be understood that the Prophet's (peace and blessings be upon him) teaching of the tashahhud to Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) was at the early time when the tashahhud was first prescribed. Later the command to send blessings upon the Prophet (peace and blessings be upon him) came. The proof of this is the Companions' saying: 'Qad 'arafna al-salam' (We have come to know the salam), that is, we have come to know the way of the salam, now tell us how we should send blessings upon you. Then, after that, concluding the prayer with the salam was prescribed. The salam was prescribed either together with it or some time after it. And Allah knows best. And what confirms this is the following report.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2968