Hadithcore
Mishkat al-Masabih, 2324

Al-Agharr al-Muzani reported God’s messenger as saying, “My heart is invaded by unmindfulness, and I ask God’s pardon a hundred times in the day.” Muslim transmitted it.

وَعَنِ الْأَغَرِّ الْمُزَنِيِّ رَضِيَ اللَّهُ عَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «إِنَّهُ لَيُغَانُ عَلَى قَلْبِي وَإِنِّي لَأَسْتَغْفِرُ اللَّهَ فِي الْيَوْم مائَة مرّة» . رَوَاهُ مُسلم

References1 variant
In-Book Reference
Book 9, Hadith 98