This is an issue concerning which there is a difference of opinion among the fuqaha’. Some of them are of the view that the worshipper should clench his right hand and point with his index finger in the sitting between the two prostrations as he does during the tashahhud, and some of them say that he should stretch out his hand and not clench it.
Ibn al-Qayyim (may Allaah have mercy on him) said: Then he (blessings and peace of Allaah be upon him) raised his head, saying takbeer but not raising his hands, and he lifted his head from prostration before his hands, then he sat muftarishan, spreading out his left foot and sitting on it, and holding his right foot upright. Al-Nasaa’i narrated that Ibn ‘Umar said: One of the Sunnahs of prayer is to hold the right foot upright with the toes facing towards the qiblah and to sit on the left foot. And there is no report to suggest that the Prophet (blessings and peace of Allaah be upon him) sat at this point in the prayer in any other way.
And he would place his hands on his thighs and place his elbows on his thighs and the ends of his fingers on his knees, and he would clench two of this fingers and make a circle, then he would raise his finger, supplicating with it and moving it. This was said by Waa’il ibn Hajar. Then he would say between the two prostrations: “O Allaah, forgive me, have mercy on me, help me, guide me and grant me provision.” This is how Ibn ‘Abbaas (may Allaah be pleased with him) narrated it from him (blessings and peace of Allaah be upon him). Hudhayfah stated that he used to say: “Lord forgive me, Lord forgive me.” End quote from Zaad al-Ma’aad, 1/230
Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said:
With regard to the left hand, it should be laid flat with all the fingers hand close together and pointing towards the qiblah and the edge of the elbow should be at the end of the thigh, meaning that he should not hold it away from the body; rather it should be resting on the thigh.
As for the right hand, the Sunnah indicates that he should clench the pinkie finger and ring finger, make a circle with the thumb and middle finger, and raise the forefinger, moving it when saying the du’aa’. This is what it says in the reports from Imam Ahmad of the hadeeth of Waa’il ibn Hajar, with an isnaad of which the author of al-Fath al-Rabbaani said is jayyid. The commentator on Zaad al-Ma’aad said that it is saheeh, and that was also the view of Ibn al-Qayyim.
As for the fuqaha’, they said that the right hand should be laid flat when sitting between the two prostrations, like the left hand, but following the Sunnah is better, and it is not narrated in the Sunnah in any hadeeth, whether it be saheeh (sound), da’eef (weak) or hasan (good) that the right hand should be spread out on the right thigh. Rather it is narrated that it should be clenched; the pinkie finger and ring finger should be clenched, and a circle should be made with the thumb and middle finger, or the middle finger should also be clenched, and the thumb should be clenched with it when sitting in prayer. Thus it was narrated in general terms, and in some versions it says, “when he sits for the tashahhud.” Both versions appear in Saheeh Muslim. So when we take the phrase “when he sits in prayer”, we say: This is general and applies to all sittings, and the words “when he sits for the tashahhud” in some versions do not refer to that specific point in the prayer, because we have a principle which was mentioned by the scholars of usool, and among those who always mentioned it was al-Shawkaani in Nayl al-Awtaar and al-Shanqeeti in Adwa’ al-Bayaan, among others, who say that if there is a report stating that the ruling is broadly application and there is another report which mentions that ruling in a specific situation, that does not mean that the second report is specifying and limiting the application of the ruling mentioned in the first report; rather the specifying and limiting is to be understood as applying when a report refers to specific situations with a ruling different from that which is applicable in regular situations.
An example of the first is if I tell you: honour the students. This is general in meaning and includes all students. Then I tell you: honour So and so - who is one of the students. Does this imply that I should not honour other students? The answer is no, but it implies that there is a particular reason why I singled him out for mention.
And an example of the second is if I say: honour the students, then I say: do not honour So and so - who is one of the students. This is specifying, because in the first case I mentioned So and so so as to apply a ruling to him that is applicable to everyone, because he is one of the students, but in the second case, I mentioned him so as to apply a ruling different from the ruling that is applicable to everyone. Hence they say when defining specification in the context of a ruling that is different or when excluding some from that ruling: therefore a different ruling must be applied to them. But if the ruling that applies to these is the same ruling as is applicable to the others, the majority of scholars of usool think that it does not indicate exclusivity for this group, as stated by the author of Adwa’ al-Bayaan. This is clear, as in the examples that we have given. Based on this, the fact that some of the versions of the hadeeth of Ibn ‘Umar which refer to clenching the hand in the tashahhud only does not mean that this is the only point in the prayer in which that is to be done, because there are other reports which state that this is to be done in any sitting in the prayer. End quote from al-Sharh al-Mumti’, 3/177.
Thus the evidence for this issue, and where it is to be found in al-Sharh al-Mumti’, is clear to you.
And Allaah knows best.