كتاب الأشربة
36  
The Book of Drinks
(17)
Chapter: It is recommended to pass water and milk etc., to the right of the one who drinks first
(17)
باب اسْتِحْبَابِ إِدَارَةِ الْمَاءِ وَاللَّبَنِ وَنَحْوِهِمَا عَنْ يَمِينِ الْمُبْتَدِئِ ‏‏
Sahih Muslim 2029 a

Anas b. Malik reported that there was brought to Allah's Messenger (ﷺ) a cup of milk mixed with water, while there was on his right a desert Arab and on his left Abu Bakr. He (the Holy Prophet) drank; he then gave it to the desert Arab and said:

(Give to one) who is on the right, then again who is on the right.
حَدَّثَنَا يَحْيَى بْنُ يَحْيَى، قَالَ قَرَأْتُ عَلَى مَالِكٍ عَنِ ابْنِ شِهَابٍ، عَنْ أَنَسِ بْنِ مَالِكٍ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم أُتِيَ بِلَبَنٍ قَدْ شِيبَ بِمَاءٍ وَعَنْ يَمِينِهِ أَعْرَابِيٌّ وَعَنْ يَسَارِهِ أَبُو بَكْرٍ فَشَرِبَ ثُمَّ أَعْطَى الأَعْرَابِيَّ وَقَالَ ‏ "‏ الأَيْمَنَ فَالأَيْمَنَ ‏"‏ ‏.‏
Reference : Sahih Muslim 2029a
In-book reference : Book 36, Hadith 163
USC-MSA web (English) reference : Book 23, Hadith 5032
  (deprecated numbering scheme)