بُلُوغُ الْمَرَامِ
Bulugh al-Maram 468
The Book of Prayer
وَعَنْ سَمُرَةَ بنِ جُنْدُبٍ - رضى الله عنه - { أَنَّ اَلنَّبِيَّ - صلى الله عليه وسلم -كَانَ يَسْتَغْفِرُ لِلْمُؤْمِنِينَ وَالْمُؤْمِنَاتِ كُلَّ جُمُعَةٍ } رَوَاهُ اَلْبَزَّارُ بِإِسْنَادٍ لَيِّن ٍ [1] .
Narrated Samurah bin Jundub (RA): The Prophet (ﷺ) used to ask for (Allah's) forgiveness for the believing men and believing women, every al-Jumu'ah (Friday prayer). [al-Bazzar reported it through a weak chain of narrators].
Sunnah.com reference: Book 2, Hadith 390