Mu'adh bin Jabal said:
"When the Messenger of Allah (ﷺ) sent me to Yemen, he said: 'Do not pass any judgment or make any decision except on the basis of what you know. If you are uncertain about a matter, wait until you understand it fully, or write to me concerning it.'" (Maudu') (ID)
English reference (ID): Vol. 1, Book 1, Hadith 55 (ID)
Arabic reference (ID): Book 1, Hadith 57 (ID)