Five other reliable transmitters also corroborated Abu Salih with reports similar to Sumayy’s report from him; all of their versions contain the third addition. I have documented their hadiths in detail in the full version of my work, Sifat Salat al-Nabi (The Prophet’s Prayer Described), explaining the variations in some of their wordings; I have also documented them briefly in al-Irwa’ (2/62/344).
Now that you know this, one point that should be noted is that the second addition—“he will be forgiven ...”—appears in Ahmad and al-Bayhaqi with the wording:
“Those in the mosque will be forgiven!”
Al-Hafiz al-Mundhiri attributed it in al-Targhib (1/177/1) to al-Nasa’i. Yet I did not find it in either his Sunan al-Sughra or his Sunan al-Kubra. In both works, he transmitted it with the first wording through most of the routes mentioned above, in addition to the route of Sumayy from Abu Salih. Perhaps the mention of al-Nasa’i there is an error by one of the copyists, or a slip of the author’s mind or pen. I have encountered such matters in my new critical edition of that work, which is currently in press. Perhaps the correct attribution is al-Bayhaqi or Ahmad in place of al-Nasa’i. And Allah knows best.
Moreover, in this wording it is, in my view, extremely rejected, since it contradicts the first wording, which is mass-transmitted from Abu Hurayrah, may Allah be pleased with him. It is apparent that Muhammad ibn Ubayd—al-Tanafisi—is the hidden defect, for he was inconsistent in transmitting it: at times he narrated it with the wording reported by the main body of transmitters, “he will be forgiven”—which is why Abu Awanah included it in his Sahih through his route—and at other times he narrated it with the contradictory wording. It therefore appears to me that this Ibn Ubayd, despite the hadith critics’ agreement on his reliability, had some misconceptions. This is why Imam Ahmad, as his son Salih related from him, said:
“He openly adhered to the sunnah, but he made mistakes and did not retract his mistakes.”
As recorded in Tahdhib al-Tahdhib.