Once Messenger of Allah ﷺ visited us in this house of ours and asked for something to drink. We milked one of our sheep and mixed it with water from this well of ours and gave it to him. Abu Bakr was sitting on his left side and ʿUmar in front of him and a bedouin on his right side. When Messenger of Allah ﷺ finished, ʿUmar said to Messenger of Allah ﷺ "Here is Abu Bakr." But Messenger of Allah ﷺ gave the remaining milk to the bedouin and said twice, "The (persons on the) right side! So, start from the right side." Anas added, "It is a Sunna (the Prophet's traditions)" and repeated it thrice.  

سَمِعْتُ أَنَسًا ؓ يَقُولُ أَتَانَا رَسُولُ اللَّهِ ﷺ فِي دَارِنَا هَذِهِ فَاسْتَسْقَى فَحَلَبْنَا لَهُ شَاةً لَنَا ثُمَّ شُبْتُهُ مِنْ مَاءِ بِئْرِنَا هَذِهِ فَأَعْطَيْتُهُ وَأَبُو بَكْرٍ عَنْ يَسَارِهِ وَعُمَرُ تُجَاهَهُ وَأَعْرَابِيٌّ عَنْ يَمِينِهِ فَلَمَّا فَرَغَ قَالَ عُمَرُ هَذَا أَبُو بَكْرٍ فَأَعْطَى الأَعْرَابِيَّ ثُمَّ قَالَ الأَيْمَنُونَ الأَيْمَنُونَ أَلاَ فَيَمِّنُوا قَالَ أَنَسٌ فَهْىَ سُنَّةٌ فَهْىَ سُنَّةٌ ثَلاَثَ مَرَّاتٍ  

A tumbler (full of milk or water) was brought to the Prophet ﷺ who drank from it, while on his right side there was sitting a boy who was the youngest of those who were present and on his left side there were old men. The Prophet ﷺ asked, "O boy, will you allow me to give it (i.e. the rest of the drink) to the old men?" The boy said, "O Messenger of Allah ﷺ! I will not give preference to anyone over me to drink the rest of it from which you have drunk." So, the Prophet ﷺ gave it to him.  

أُتِيَ النَّبِيُّ ﷺ بِقَدَحٍ فَشَرِبَ مِنْهُ وَعَنْ يَمِينِهِ غُلاَمٌ أَصْغَرُ الْقَوْمِ وَالأَشْيَاخُ عَنْ يَسَارِهِ فَقَالَ يَا غُلاَمُ أَتَأْذَنُ لِي أَنْ أُعْطِيَهُ الأَشْيَاخَ قَالَ مَا كُنْتُ لأُوثِرَ بِفَضْلِي مِنْكَ أَحَدًا يَا رَسُولَ اللَّهِ فَأَعْطَاهُ إِيَّاهُ