It was narrated from Anas bin Malik that the Messenger of Allah (ﷺ) said:
"Seeking knowledge is a duty upon every Muslim, and he who imparts knowledge to those who do not deserve it, is like one who puts a necklace of jewels, pearls and gold around the neck of swines." (ID)
English reference (ID): Vol. 1, Book 1, Hadith 224 (ID)
Arabic reference (ID): Book 1, Hadith 229 (ID)