(44) The Book of Financial Transactions
كتاب البيوع
(54) Chapter: Allowing more when weighing goods for sale
(54) باب الرُّجْحَانِ فِي الْوَزْنِ ‏‏
Sunan an-Nasa'i 4592 
It was narrated that Suwaid bin Qais said:
"Makhrafah Al-Abdi and I brought some cloth from Hajar, and the Messenger of Allah came to us while we were in Mina where there w a man who weighed (goods) in return for payment. He bought some trousers from us, and said to the man who weighed: 'Weigh it, and allow more."'
أَخْبَرَنَا يَعْقُوبُ بْنُ إِبْرَاهِيمَ، قَالَ حَدَّثَنَا عَبْدُ الرَّحْمَنِ، عَنْ سُفْيَانَ، عَنْ سِمَاكٍ، عَنْ سُوَيْدِ بْنِ قَيْسٍ، قَالَ جَلَبْتُ أَنَا وَمَخْرَفَةُ الْعَبْدِيُّ، بَزًّا مِنْ هَجَرَ فَأَتَانَا رَسُولُ اللَّهِ صلى الله عليه وسلم وَنَحْنُ بِمِنًى وَوَزَّانٌ يَزِنُ بِالأَجْرِ فَاشْتَرَى مِنَّا سَرَاوِيلَ فَقَالَ لِلْوَزَّانِ ‏ "‏ زِنْ وَأَرْجِحْ ‏"‏ ‏.‏
Grade :  Sahih (Darussalam)
Reference : Sunan an-Nasa'i 4592
In-book reference : Book 44, Hadith 144
English translation : Vol. 5, Book 44, Hadith 4596