It is narrated from Husayn bin Abd al-Rahman that we came to Ibrahim, and Amr bin Murrah related to him: We prayed in the mosque of the Hadramis, and Alqamah bin Wa'il narrated to me from his father that he saw the Messenger of Allah (peace and blessings be upon him) raise both his hands (that is, perform raf' al-yadayn) when beginning the prayer, and when he bowed he also raised his hands. Ibrahim said: I do not think (suppose) that Alqamah's father (Wa'il) saw the Messenger of Allah (peace and blessings be upon him) on any day other than that day, so he memorised that, while Abdullah (may Allah be pleased with him) did not retain it from him. Then Ibrahim said: Raising the hands is only at the beginning of the prayer.
(b) Abu Bakr bin Ishaq al-Faqih said: This is a defect not worth listening to, because raising the hands is established from the Prophet (peace and blessings be upon him), then from the Rightly Guided Caliphs (may Allah be pleased with them), then from the Companions (may Allah be pleased with them) and the Successors as well. And the forgetfulness of Abdullah bin Mas'ud (may Allah be pleased with him) is not only about raising the hands, which the other Companions (may Allah be pleased with them) saw the Prophet (peace and blessings be upon him) do; rather, Ibn Mas'ud (may Allah be pleased with him) forgot many other things besides. For example, he forgot something from the Qur'an about which the Muslims have never differed, namely the Mu'awwidhatayn. Likewise Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) fell into forgetfulness regarding something all the scholars agree was abrogated and abandoned, namely tatbiq, and regarding how two men should stand behind the imam; he also forgot, in a matter on which the scholars have no disagreement, that the Prophet (peace and blessings be upon him) prayed the morning prayer on the day of Eid al-Adha at its proper time. Likewise he forgot how the Prophet (peace and blessings be upon him) combined (the prayers) at Arafah. He also forgot the agreed matter that in prostration in prayer the elbows and forearms are kept off the ground, and he forgot how the Messenger of Allah (peace and blessings be upon him) used to recite "And (by) He who created the male and the female" [Surah al-Layl: 3]. And since it is correct of Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that he forgot things like this in prayer, it is possible that he forgot raising the hands as well.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2536