Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions. Bukhari reported that Malik bin Harith was asked about the prayer of the Prophet (Sallallahu Alaihi wa Sallam). He said, "It was like the prayer of our Sheikh Amr Ibn Salama .’ Ayyoob said, The latter used to pronounce the Takbeer perfectly (pronouncing Allahu Akbar) when he raises from the second prostration sits for a while and then supports himself on the ground and gets up."
Imam Al Bukhari mentioned this Hadith under the chapter entitled “Supporting oneself while getting up from prostration”.
Al Hafiz Ibn Hajar said in ‘Al-Fath’, 'the purpose of this title is to highlight the action of clenching one’s fists on the earth at the time of getting up from the prostration or at the time of sitting.'
What was reported from Ali and which is referred to by Ibn Qudamah that he said, “'It is Sunnah in prayer that when one stands up during the first two Rak’ah, he/she should not clench his fists on the earth except if one is aged and cannot stand without supporting himself/herself.' [Reported by Imam Al Bukhari and Ibn Abi Shaibah] is weak as Sheikh Al Albani mentioned in Silsilah Al-Dha’efa. Also it is contrary to the sound Hadith that Al-Azraq bin Qais said, 'I saw Ibn Umar performing prayer, when he got up from the second Rak’ah he put his hand on the earth and leaned on them to get up. I said to his sons and his companions, perhaps he is doing so due to his old age. They said, ‘No, this is the usual way of performing prayer.’' [Al Baihaqi with a sound chain]
Abu Ishaqh al-Harabi reported in his book ‘Garib al-Hadith’ from Al Azraq bin Qais who said, 'I saw Ibn Umar performing prayer, when he got up he would clench his fists (like the one who kneads dough). I asked him about this action, he said, ‘I saw the Prophet (Sallallahu Alaihi wa Sallam) doing the same.' [The chain is Hasan (acceptable)]
Allah knows best.