Tirmidhi

Fiqh al-Hadith
↰ Imam Tirmidhi rahimahullah has graded this hadith as “hasan sahih.”
Imam Ibn al-Jarud rahimahullah (215) and Hafiz Nawawi rahimahullah [خلاصة الاحكام : 508/1] have declared it “sahih.”

«ان عطأ أن موسٰي بن عبدالله بن جميل الجمحي سلم على ابن عباس، و هو يصلي، فأ خذه بيده۔»
‘Ata ibn Abi Rabah rahimahullah narrates that Musa ibn Abdullah ibn Jamil Jumahi greeted (said salam to) our master Ibn Abbas radi Allahu anhuma; he was in prayer, and he (Ibn Abbas) took hold of his hand (this was his way of replying to the salam). [الشمس الكبري للبيهقي 259/2، مصنف ابن ابي شيبة : 73/2، سنده صحيح]

Lexical Explanation:
«يَرُدُّ عَلَيْهِمْ» In "alayhim," the pronoun "hum" refers to the people of Quba.
«يَقُولُ هٰكَذَا» He would do so practically or indicate it. Here, "qawl" is used in the sense of "action." This often occurs in Arabic speech.
«وَبَسَطَ كَفَّهُ» Stretched, spread out.

Benefits and Issues:
➊ This hadith is evidence that responding to greetings (salam) during prayer with a gesture is legislated. Many scholars hold this view. There are also some who consider responding to salam during prayer to be prohibited. They believe that this refers to a time when replying during prayer was permissible. Later, when speaking and conversing during prayer was made forbidden, from that point onward, replying to salam also became forbidden, because this gesture is considered meaningful speech. However, it is worth considering that if this were the case—when replying to salam during prayer was permissible—then what need was there to reply with a gesture?
➋ The prohibition of conversation and the permissibility of replying to salam with a gesture is evidence that when speaking during prayer became forbidden, at that time replying with a gesture was allowed. The correct view is that, without any doubt or hesitation, replying to salam with a gesture during prayer is permissible.
➌ This hadith shows that it is correct and permissible for someone entering from outside to greet those engaged in prayer, but the reply should not be verbal; rather, it should be given by gesture.
➍ What should be the nature of this gesture? In this regard, from the hadith of Sayyiduna Suhayb radi Allahu anhu in Musnad Ahmad and the hadith of Sayyiduna Ibn Umar radi Allahu anhu in Jami‘ al-Tirmidhi, it is known that he (sallallahu alayhi wa sallam) would reply to salam with a gesture of the hand or finger. See [مسند أحمد 102، و جامع الترمذي، الصلاة، باب ماجاء فى الإشارة فى الصلاة، حديث : 368]