Sunan an-Nasa'i, Hadith 3685 ⓘ
An-Nu'man bin Bashir said: "My father took me to the Prophet to ask him to bear witness to something that he had given to me. He said: 'Do you have any other children?' He said: 'Yes.' He gestured with his hand held horizontally like this, (saying): 'Why don't you treat them all equally?'"
أَخْبَرَنَا عُبَيْدُ اللَّهِ بْنُ سَعِيدٍ، عَنْ يَحْيَى، عَنْ فِطْرٍ، قَالَ حَدَّثَنِي مُسْلِمُ بْنُ صُبَيْحٍ، قَالَ سَمِعْتُ النُّعْمَانَ بْنَ بَشِيرٍ، يَقُولُ ذَهَبَ بِي أَبِي إِلَى النَّبِيِّ صلى الله عليه وسلم يُشْهِدُهُ عَلَى شَىْءٍ أَعْطَانِيهِ فَقَالَ " أَلَكَ وَلَدٌ غَيْرُهُ " . قَالَ نَعَمْ . وَصَفَّ بِيَدِهِ بِكَفِّهِ أَجْمَعَ كَذَا أَلاَ سَوَّيْتَ بَيْنَهُمْ .
also referenced under: Book 31, Hadith 14 (In-Book) & Volume 4, Book 31, Hadith 3715 (DarusSalam)