It was narrated from Samurah bin Jundub that:
The Prophet (ﷺ) said: '"Whoever narrated a Hadith from me thinking it to be false, then he is one of the two liars." (PT)
English reference (PT): Vol. 1, Book 1, Hadith 39 (PT)
Arabic reference (PT): Book 1, Hadith 40 (PT)