كتاب الإمارة
33  
The Book on Government
(5)
Chapter: The virtue of a just ruler and the punishment of a tyrant; Encouragement to treat those under one's authority with kindness and the prohibition against causing them hardship
(5)
باب فَضِيلَةِ الإِمَامِ الْعَادِلِ وَعُقُوبَةِ الْجَائِرِ وَالْحَثِّ عَلَى الرِّفْقِ بِالرَّعِيَّةِ وَالنَّهْيِ عَنْ إِدْخَالِ الْمَشَقَّةِ عَلَيْهِمْ
Sahih Muslim 142 h

It has been narrated on the authority of Abu al-Aswad who said:

My father related to me that Ma'qil b. Yasir fell ill. 'Ubaidullah b. Ziyad called on him to inquire after his health. Here follows the tradition as narrated by Hasan from Ma'qil.
وَحَدَّثَنَا عُقْبَةُ بْنُ مُكْرَمٍ الْعَمِّيُّ، حَدَّثَنَا يَعْقُوبُ بْنُ إِسْحَاقَ، أَخْبَرَنِي سَوَادَةُ بْنُ أَبِي، الأَسْوَدِ حَدَّثَنِي أَبِي أَنَّ مَعْقِلَ بْنَ يَسَارٍ، مَرِضَ فَأَتَاهُ عُبَيْدُ اللَّهِ بْنُ زِيَادٍ يَعُودُهُ ‏.‏ نَحْوَ حَدِيثِ الْحَسَنِ عَنْ مَعْقِلٍ، ‏.‏
Reference : Sahih Muslim 142h
In-book reference : Book 33, Hadith 31
USC-MSA web (English) reference : Book 20, Hadith 4503
  (deprecated numbering scheme)