Narrated Anas: When Um Sulaim gave birth to a child. she said to me, "O Anas! Watch this boy carefully and do not give him anything to eat or drink until you have taken him to the Prophet (ﷺ) tomorrow morning for the Tahnik." So the next morning I took the child to the Prophet (ﷺ) who was sitting in a garden and was wearing a Huraithiya Khamisa and was branding the she-camel on which he had come during the Conquest of Mecca.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنِي مُحَمَّدُ بْنُ الْمُثَنَّى، قَالَ حَدَّثَنِي ابْنُ أَبِي عَدِيٍّ، عَنِ ابْنِ عَوْنٍ، عَنْ مُحَمَّدٍ، عَنْ أَنَسٍ ـ رضى الله عنه ـ قَالَ لَمَّا وَلَدَتْ أُمُّ سُلَيْمٍ قَالَتْ لِي يَا أَنَسُ انْظُرْ هَذَا الْغُلاَمَ فَلاَ يُصِيبَنَّ شَيْئًا حَتَّى تَغْدُوَ بِهِ إِلَى النَّبِيِّ صلى الله عليه وسلم يُحَنِّكُهُ. فَغَدَوْتُ بِهِ، فَإِذَا هُوَ فِي حَائِطٍ وَعَلَيْهِ خَمِيصَةٌ حُرَيْثِيَّةٌ، وَهْوَ يَسِمُ الظَّهْرَ الَّذِي قَدِمَ عَلَيْهِ فِي الْفَتْحِ.
sunnah.com