The Messenger of Allah ﷺ prayed one of the afternoon prayers as five units. He was asked, "Has there been an addition to the prayer?"He replied, "What do you mean?"They said, "You prayed five units."He said, "I am only a human being. I forget as you forget, and I remember as you remember."Then he performed two prostrations and turned away.
أخبرنا سويد بن نصر قال أنبأنا عبد الله عن أبي بكر النهشلي عن عبد الرحمن بن الأسود عن أبيه
أن رسول الله ﷺ صلى إحدى صلاتي العشي خمسا فقيل له أزيد في الصلاة قال وما ذاك قالوا صليت خمسا قال إنما أنا بشر أنسى كما تنسون وأذكر كما تذكرون فسجد سجدتين ثم انفتل
[Sahih] Reported by Muslim, Mosques, Chapter on forgetfulness in prayer and sujud for it, no. 93/572, from the hadith of Abu Bakr Nahshali, through him. It is also in al-Kubra, no. 1182, and the hadith has supporting narrations.