I saw Ibn Umar raising his hands every time he bowed and every time he raised his head from bowing.Ati said, I asked him, "What is this?"He replied, "When the Prophet ﷺ would stand for two units of prayer, he would say the takbir and raise his hands."
حدثنا محمد بن فضيل عن عاصم بن كليب
رأيت ابن عمر يرفع يديه كلما ركع وكلما رفع رأسه من الركوع قال فقلت له ما هذا قال كان النبي ﷺ إذا قام في الركعتين كبر ورفع يديه
Its chain of transmission is sahih. Muhammad bin Fudayl bin Ghazwan, his reliability was established previously at 890, and he is among the early teachers of Ahmad, who died in the year 195. Ibn Madini said, "He was thiqa, firmly reliable in hadith," and Bukhari gave his biography in al-Kabir 1/1/207,208.Asim bin Kulayb bin Shihab al-Jarmi, his reliability was established previously at 85, and we add here the statement of Abu Dawud, "He was among the devout worshippers," and he said, "He was the most excellent of the people of Kufa." Ibn Abu Hatim gave his biography in al-Jarh wal-Tadil 3/1/349, 350.In H here it appears as, "from Asim, from Ibn Kulayb," which is a pure printing error. We have corrected it from K and M and from what we will mention regarding the sourcing of the hadith.The hadith was narrated, with only its final marfu portion, by Abu Dawud 1:271, from Uthman bin Abu Shayba and Muhammad bin Ubayd al-Muharibi, both of them from Muhammad bin Fudayl, with this chain of transmission. Munziri did not attribute it, at 712, to any other book. Likewise, Ibn Hazm narrated it in al-Muhalla 4:90 by way of Abu Dawud.As for the story at the beginning of the hadith here, concerning Muharib bin Dithar seeing Ibn Umar and questioning him, I have not found it anywhere else.His statement in the marfu hadith, "when he rose in the two rakats," means, when he rose for the third rakat after the first two rakats and the first tashahhud. This meaning has come up repeatedly from the hadith of Ibn Umar through other routes, both at length and in brief, the most recent being 6175.The wording of the story and the hadith here indicates that it too is abridged, since the answer does not correspond to the question. But it is understood that he means the raising of the hands at the ruku, at rising from it, and at standing up for the third rakat, as is self-evident, and as is established through the most sahih chains from Ibn Umar, as has come before in the Musnad, and with the two Shaykhs and others. See al-Muntaqa 845–849.