Al-Ghazali reported: A man came to Abdullah ibn al-Mubarak, may Allah have mercy on him, and he complained about disrespect from his son. Ibn al-Mubarak said, “Have you supplicated against him?” The man said yes. Ibn al-Mubarak said, “You have corrupted him.” Al-Ghazali said, “It is recommended to be gentle with children.”
Source: Iḥyā’ Ulūm al-Dīn 2/217
عن الغزالي جَاءَ رَجُلٌ إِلَىٰ عَبْدِ اللهِ بْنِ الْمُبَارَكِ رَحِمَهُ اللهُ يَشْكُو إِلَيْهِ عُقُوقَ وَلَدِهِ فَسَأَلَهُ إِبْنُ الْمُبَارَكِ أَدَعَوْتَ عَلَيْهِ قَالَ نَعَمْ قَالَ أَنْتَ أَفْسَدْتَهُ وَقال الغزالي وَيُسْتَحَبُّ الرِّفْقُ بِالْوَلَدِ
2/217 إحياء علوم الدين