Forgetfulness in prayer

It is narrated from Humayd bin Tarkhan that Abdullah bin Shaqiq led us in the Asr prayer, and he made us perform two prostrations (of forgetfulness, at the end of the prayer), although we had not noticed any forgetfulness or mistake in his prayer. When he gave the salam, the people mentioned this to him and said: "We did not notice any forgetfulness or mistake (in your prayer) (so why did you make these prostrations)?" He replied: "In fact, I was talking to myself (during the prayer) (i.e. my attention had wandered, so I made these prostrations as a precaution)."
The chain of this report is sahih (authentic), and it describes the practice of an eminent Successor regarding performing the prostration of forgetfulness when whisperings or thoughts arise during the prayer.

Abd al-Rahman bin Shimasah relates that Sayyiduna Amr bin al-As (may Allah be pleased with him) led the people in prayer, and he stood up (forgetfully) instead of sitting for the (first) tashahhud. The people called out to him loudly to alert him, saying: 'Subhan Allah, Subhan Allah' (Glory be to Allah, Glory be to Allah), but he remained as he was and continued the prayer. When he had completed his prayer, he made two prostrations (of forgetfulness), then said: "O people, what you wanted to point out to me was not hidden from me, and nothing prevented me from sitting (for the tashahhud) except what I did in following the Sunnah (that after rising to standing one does not go back)."
It is also narrated from Abd al-Rahman bin Shimasah that Sayyiduna Uqbah bin Amir (may Allah be pleased with him) likewise stood up in his prayer (leaving the tashahhud), and then the narrator mentioned an incident similar to it.

It is narrated from Sayyiduna Sa'd bin Abi Waqqas (may Allah be pleased with him) that he stood up after two rak'ahs (forgetfully, instead of sitting for the tashahhud), and the people said Subhan Allah to alert him, but he stood fully upright. Then, completing the prayer, he made the two prostrations of forgetfulness before giving the salam, and said: "Did you think that I would sit? Indeed, I did just as I saw the Messenger of Allah (peace and blessings be upon him) doing."
Imam Ahmad bin Mani' transmitted it through Abu Mu'awiyah, and Amr bin Muhammad al-Naqid said: I have not heard anyone other than Abu Mu'awiyah narrate this hadith as marfu' (as the Prophet's own action).
Waki' narrated it through Isma'il as mawquf (the Companion's own action).
And al-Mughirah bin Shubayl also narrated it through Qays from Sayyiduna al-Mughirah bin Shu'bah (may Allah be pleased with him).

It is narrated from Damdam bin Jaws that I came to Sayyiduna Abu Hurayrah and Sayyiduna Abdullah bin Hanzalah (may Allah be pleased with them both) while the two of them were sitting in the mosque at the time the sun passed its zenith. Sayyiduna Abdullah bin Hanzalah (may Allah be pleased with him) related: "Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) led us in the Maghrib prayer and forgot to recite in the first rak'ah. So when he stood for the second rak'ah he recited Surah al-Fatihah and a surah, then he again recited Surah al-Fatihah and a surah (to make up for the first rak'ah), then continued his prayer until he completed it, then he made the two prostrations of forgetfulness."
Imam al-Harith bin Abi Usamah narrated this in his Musnad; this report is sahih (authentic) and indicates the method of making up for forgetting the recitation in the prayer.

It is narrated from Silah bin Ashyam (may Allah have mercy on him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever prays a prayer during which not even a thought of anything of worldly affairs passes through his heart and mind, then whatever he asks of Allah, the Mighty and Majestic, during that prayer, Allah, Glorified and Exalted, will surely grant it to him."
Imam Ahmad narrated this hadith in Kitab al-Zuhd, and its chain is mursal, since Silah bin Ashyam (may Allah have mercy on him) is an eminent Successor who narrated it directly from the Prophet (peace and blessings be upon him); however, there are supporting reports for it in other reliable hadith regarding presence of heart and humility in prayer.

It is narrated from Sayyiduna Mu'awiyah al-Sulami (may Allah be pleased with him) that Sayyiduna Mu'awiyah bin Abi Sufyan (may Allah be pleased with them both) led us in the three rak'ahs of the Maghrib prayer. He stood up after two rak'ahs (without sitting for the first tashahhud), and the people said Subhan Allah to alert him, so he gestured to them (to stand). When he had completed his prayer and given the salam, he turned to the people and addressed them, saying: "I saw the Messenger of Allah (peace and blessings be upon him) do exactly as you saw me do, and had I not seen him (peace and blessings be upon him) do it, I would never have done it."
Imam Abu Ya'la narrated it in his Musnad.

It is narrated from Sayyidah Aishah al-Siddiqah (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) said: "The two prostrations of forgetfulness suffice for every kind of addition and omission (that occurs in the prayer)." A narration with the same meaning was also transmitted by Imam Abu Kurayb through Hafs bin Bishr al-Asadi from Hakim bin Nafi'.
The narrator in the chain of this hadith, Hakim bin Nafi', is da'if (weak).