Ibn Umar reported from the Messenger of Allah ﷺ regarding the tashahhud, "All greetings belong to Allah, and prayers and good deeds. Peace be upon you, Prophet, and the mercy of Allah and His blessings."Ibn Umar said, "I added to it the words, 'and His blessings.' Peace be upon us and upon the righteous servants of Allah. I bear witness that there is no god but Allah."Ibn Umar said, "I added to it, 'alone, with no partner,' and I bear witness that Muhammad is His servant and messenger."
عن رسول الله ﷺ في التشهد: التحيات لله، الصلوات الطيبات، السلام عليك أيها النبي ورحمة الله وبركاته. - قال ابن عمر: زدت فيها: وبركاته السلام علينا وعلى عباد الله الصالحين، أشهد أن لا إله إلا الله قال ابن عمر: زدت فيها: وحده لا شريك له وأشهد أن محمدا عبده ورسوله.
Abu Dawud (971) and Daraqutni (1/351) both reported it through the hadith of Nasr bin Ali, who said, my father narrated to me, Shubah narrated to us, from Abu Bishr, who said, I heard Mujahid narrating from Ibn Umar, and he mentioned it. Its chain is sahih. Daraqutni also graded it sahih.As for Ibn Umar's statement, "I added to it 'and His blessings' and 'alone, having no partner,'" this addition was not from himself. Rather, he did not hear this from the Prophet ﷺ, but he heard it from Abu Musa Ashari. These words are found in the tashahhud of Abu Musa Ashari. What appears to be the case is that he took the shorter version from the Prophet ﷺ, and the rest from Abu Musa Ashari, and all of it is marfu, as is explained in detail in the book of prayer.