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." (FR)
English reference (FR): Vol. 1, Book 1, Hadith 39 (FR)
Arabic reference (FR): Book 1, Hadith 40 (FR)