Muwatta Malik 537

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ يَحْيَى بْنِ سَعِيدٍ، أَنَّهُ قَالَ سَمِعْتُ سَعِيدَ بْنَ الْمُسَيَّبِ، يَقُولُ صَلَّيْتُ وَرَاءَ أَبِي هُرَيْرَةَ عَلَى صَبِيٍّ لَمْ يَعْمَلْ خَطِيئَةً قَطُّ فَسَمِعْتُهُ يَقُولُ اللَّهُمَّ أَعِذْهُ مِنْ عَذَابِ الْقَبْرِ ‏.‏

Yahya related to me from Malik that Yahya ibn Said said that he heard Said ibn al-Musayyab say, "I once prayed behind Abu Hurayra over a child who had never done a wrong action and I heard him say, 'O Allah, give him protection from the torment of the grave

Reference

Muwatta Malik 537

In-book

Book 16, Hadith 18