رِيَاضُ الصَّالِحِينَ
Riyad as-Salihin 603
The Book of Miscellany
Modesty and Courtesy towards the Believers
وَعَنْ أَنَسٍ رَضِيَ اللَّهُ عَنْهُ أَنَّهُ مَرَّ عَلَى صِبْيَانٍ فَسَلَّمَ عَلَيْهِمْ وَقَالَ: كَانَ النَّبِيُّ صَلَّى اللَّه عَلَيْهِ وَسَلَّمَ يَفْعَلُهُ. ((مُتَّفَقٌ عَلَيْهِ))
Anas (May Allah be pleased with him) passed by some children and greeted them (by saying As-salamu 'alaikum to them). Then he said: The Prophet (ﷺ) used to do the same. [Al-Bukhari and Muslim].
Riyad as-Salihin, 603