It is narrated from Ali bin Abdullah bin Abbas (may Allah have mercy on him) that he said: "I prayed a prayer behind Sayyiduna Anas bin Malik (may Allah be pleased with him) in which he made an error (of forgetfulness) while leading us, so he prostrated after the salam. Then he turned towards us and said: 'Know that I have done only as I saw the Messenger of Allah (peace and blessings be upon him) doing.'"
No one narrated this hadith from Salih bin Ali bin Abdullah bin Abbas except his son, and Abu al-Tahir bin al-Sarh is alone in narrating it.
Hadith Referenceالمعجم الأوسط / باب الميم / 6516
Hadith Gradingمحدثین:إسناده ضعيف، فيه مجاهيل
Hadith Takhrij«قال الهيثمي: وفيه مجاهيل «مجمع الزوائد ومنبع الفوائد، ج 2، ص 154»» «أخرجه ابن أبي شيبة فى «مصنفه» برقم: 4470، 4478، 4498، والطحاوي فى «شرح معاني الآثار» برقم: 2570، 2571، والطبراني فى «الصغير» برقم: 437»