Maliks Muwatta Book 56, Hadith Number 16.
Section : Truthfulness and Lying.
Malik related to me that he heard that Abdullah ibn Masud used to say, “You must tell the truth. Truthfulness leads to right action. Right action leads to the Garden. Beware of lying. Lying leads to corruption, and corruption leads to the Fire. Don’t you see that it is said, ‘He speaks the truth and acts rightly,’ and, ‘He lies and is corrupt.'”