Al-Hasan bin al-Hurr also narrated a report with the same meaning as the hadith of Yahya bin Yahya; it is the same up to his words 'al-salihin', then he said: 'Ashhadu an la ilaha illallahu wa ashhadu anna Muhammadan 'abduhu wa rasuluh' (I bear witness that there is no god but Allah, and I bear witness that Muhammad (peace and blessings be upon him) is the servant of Allah and His Messenger).
Sayyiduna Abdullah (may Allah be pleased with him) says: "When you have recited this, you have completed the prayer that was obligatory upon you. (Now it is your choice:) if you wish to stand, then stand, and if you wish to sit, then sit."
Ali (may Allah have mercy on him) said: Shababah is thiqah (trustworthy); he separated the end of the hadith and made it the words of Ibn Mas'ud, and this is more correct than the narration of those who inserted its end into the words of the Prophet (peace and blessings be upon him), and Allah knows best. Abu Ali al-Husayn bin Ali al-Hafiz said: Zuhayr erred in his narration from al-Hasan bin al-Hurr and inserted into the words of the Prophet (peace and blessings be upon him) what is not from his words, namely his saying: 'When you have done this, you have completed your prayer'; this is only from Abdullah bin Mas'ud.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2966