(a) This report has also been narrated through another chain. Uthman al-Darimi said: This has been narrated from Ali through this flimsy route.
(b) Through another chain it is narrated from Sayyiduna Ali (may Allah be pleased with him) that he saw the Prophet (peace and blessings be upon him) "raising his hands when going into bowing and after raising his head from bowing."
It cannot be supposed of Sayyiduna Ali (may Allah be pleased with him) that he would prefer his own practice over the practice of the Prophet (peace and blessings be upon him). However, Abu Bakr al-Nahshali is not one whose narration is used as proof, or by whom a sunnah is established that no one else has brought.
Al-Za'farani said that Imam al-Shafi'i (may Allah have mercy on him) said in his earlier position (al-qawl al-qadim): The reports from Sayyiduna Ali (may Allah be pleased with him) and Sayyiduna Ibn Mas'ud (may Allah be pleased with him) that both of them raised their hands only at the beginning of the prayer and not otherwise are not established.
Imam al-Shafi'i (may Allah have mercy on him) said: This hadith is narrated only by Asim bin Kulayb from his father, from Sayyiduna Ali (may Allah be pleased with him). He took this narration, but left the narration that Asim took from his father, from Sayyiduna Wa'il bin Hujr (may Allah be pleased with him), namely that the Prophet (peace and blessings be upon him) "raised his hands," just as Sayyiduna Ibn Umar (may Allah be pleased with them both) narrated. And even if this report were established from Sayyiduna Ali (may Allah be pleased with him) and Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him), there could be the uncertainty that he saw them only once and they did not attend to raising the hands.
If someone were to say that the memory of this escaped them and Sayyiduna Ibn Umar (may Allah be pleased with them both) retained it, that could serve as proof for him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2535