ENOfficial
Ibn Sirin said, "We were with Abu Hurayra one night and he said, 'O Allah, forgive Abu Hurayra and his mother and whoever asks for forgiveness for both of them.'" Muhammad said, "We used to ask for forgiveness for them so that we would be included in Abu Hurayra's supplication."
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا مُوسَى، قَالَ: حَدَّثَنَا سَلاَّمُ بْنُ أَبِي مُطِيعٍ، عَنْ غَالِبٍ قَالَ: قَالَ مُحَمَّدُ بْنُ سِيرِينَ: كُنَّا عِنْدَ أَبِي هُرَيْرَةَ لَيْلَةً، فَقَالَ: اللَّهُمَّ اغْفِرْ لأَبِي هُرَيْرَةَ، وَلِأُمِّي، وَلِمَنِ اسْتَغْفَرَ لَهُمَا قَالَ لِي مُحَمَّدٌ: فَنَحْنُ نَسْتَغْفِرُ لَهُمَا حَتَّى نَدْخُلَ فِي دَعْوَةِ أَبِي هُرَيْرَةَ.
sunnah.com