'Abdullah bin Mubarak said:
"If one becomes a judge or arbitrator, then they should always follow that which has been narrated." (RU)
App reference (RU): Book 56, Hadith 9 (RU)
English reference (RU): Book 55, Hadith 396 (RU)
Arabic reference (RU): Book 56, Hadith 414 (RU)