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Asma' bint 'Ubayd said, "I said to Ibn Sirin, 'I have an orphan in my care.' He said, 'Treat him as you would treat your own child. Beat him as you would beat your own child.'"
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا مُوسَى، قَالَ: حَدَّثَنَا سَلاَّمُ بْنُ أَبِي مُطِيعٍ، عَنْ أَسْمَاءَ بْنِ عُبَيْدٍ قَالَ: قُلْتُ لِابْنِ سِيرِينَ: عِنْدِي يَتِيمٌ، قَالَ: اصْنَعْ بِهِ مَا تَصْنَعُ بِوَلَدِكَ، اضْرِبْهُ مَا تَضْرِبُ وَلَدَكَ.
sunnah.com