Alqama took me by the hand and told me that Abdullah bin Masud took him by the hand, and that the Messenger of Allah ﷺ took Abdullah by the hand and taught him the tashahhud in the prayer. He then mentioned the same supplication as in the hadith of Amash, adding, "When you have said this, or completed this, you have completed your prayer. If you wish to stand, then stand, and if you wish to remain seated, then remain seated."
حدثنا عبد الله بن محمد النفيلي حدثنا زهير حدثنا الحسن بن الحر
أخذ علقمة بيدي فحدثني أن عبد الله بن مسعود أخذ بيده وأن رسول الله ﷺ أخذ بيد عبد الله فعلمه التشهد في الصلاة فذكر مثل دعاء حديث الأعمش إذا قلت هذا أو قضيت هذا فقد قضيت صلاتك إن شئت أن تقوم فقم وإن شئت أن تقعد فاقعد
[Its chain of transmission is sahih] Ahmad reported it, 1/422, from the hadith of Zuhayr through this route, and Ibn Hibban graded it sahih (al-Ihsan), 1958-1960. Its basis is found in Nasai, no. 1168. As for his statement "when you say this," it is mudraj (an interpolation) by agreement of the memorizing scholars. See al-Mudraj ila al-Mudraj by Suyuti, p. 20, and Awn al-Mabud, 1/367, from the statement of Ibn Masud