بُلُوغُ الْمَرَامِ
Bulugh al-Maram 338
The Book of Prayer
وَعَنْ عُمَرَ رَضِيَ اَللَّهُ عَنِ النَّبِيِّ - صلى الله عليه وسلم -قَالَ : { لَيْسَ عَلَى مَنْ خَلَفَ اَلْإِمَامَ سَهْوٌ فَإِنْ سَهَا اَلْإِمَامُ فَعَلَيْهِ وَعَلَى مَنْ خَلْفَهُ" } رَوَاهُ اَلْبَزَّارُ وَالْبَيْهَقِيُّ بِسَنَدٍ ضَعِيفٍ . [1]
Narrated 'Umar (RA): The Prophet (ﷺ) said: "There is no (prostrations of) forgetfulness for one who is led (in prayer) by an Imam, but when the Imam forgets, both should then make prostrations due to forgetfulness." [al-Bazzar and al-Baihaqi reported it through a weak chain of narrators].
Sunnah.com reference: Book 2, Hadith 239