Our hands in prayer, and he said: "What is the matter with them, raising their hands in prayer as if they were the tails of restive horses? Be still in prayer." (1)

1185 - Ahmad ibn Sulayman informed us, saying: Yahya ibn Adam narrated to us, from Mis'ar, from Ubaydullah ibn al-Qibtiyyah, from Jabir ibn Samurah, who said: We used to pray behind the Prophet, peace and blessings be upon him, and we would make the taslim with our hands, so he said: "What is the matter with these people, making the taslim with their hands as if they were the tails of restive horses? Is it not enough for one of them—"

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(1) Its chain is authentic. 'Abthar: he is Ibn al-Qasim al-Zubaydi, and al-A'mash: he is Sulayman ibn Mihran.
It is in "Al-Sunan al-Kubra" under numbers (557) and (1108).
Also narrated by Ahmad (20875), (20958), (20964), and (21027), Muslim (430), Abu Dawud (912) and (1000), and Ibn Hibban (1878) and (1879) via multiple paths from al-A'mash, with this chain.
It will follow below and under numbers (1318) and (1326) via the path of Ubaydullah ibn al-Qibtiyyah, from Jabir ibn Samurah, with it.
Al-Sindi said: His words "raising our hands" mean: with the taslim; for this reason he followed it with the second narration. And "al-shums" — with a damma then a sukun, or with two dammas — is the plural of shamus: meaning the animal that shies away, due to its restlessness and sharpness, and its tail is in constant agitation. The intent is the prohibition of gesturing with the hand during the taslim. "We would make the taslim" — as in the following narration — meaning: in prayer, and by this narration it becomes clear that the hadith is directed at prohibiting the raising of hands during the taslim as a gesture to both sides, and there is no indication in it of prohibiting the raising at the bowing (ruku') or at raising from it. For this reason al-Nawawi said: Using it as evidence for prohibiting the raising at the bowing and at raising from it is a reprehensible ignorance. And it may be said: consideration is given to the generality of the wording, and the wording: "What is the matter with them, raising their hands in prayer" up to his words: "Be still in prayer" is complete, so building the inference upon it is sound, and the specificity of the occasion is not to be considered — unless it is said that this applies when nothing opposes the generality, otherwise it is interpreted according to the specificity of the occasion. And here, the raising at the bowing and at raising from it has been authentically and firmly established with an irrefutable establishment, so this wording must be interpreted according to the specificity of the occasion, as a reconciliation and to ward off contradiction. I say — meaning al-Sindi: Among the reasons for refraining from indicating tawhid in the tashahhud is that it contradicts stillness; this was derived from this narration, namely the wording: "Be still in prayer." And Allah, the Exalted, knows best.
(2) In (M): "ma" (what).