Maliks Muwatta Book 56, Hadith Number 19.

Malik related to me that Safwan ibn Sulaym said, “The Messenger of Allah, may Allah bless him and grant him peace, was asked, ‘Can the mumin be a coward?’ He said, ‘Yes.’ He was asked, ‘Can the mumin be a miser?’ He said, ‘Yes.’ He was asked, ‘Can the mumin be a liar?’ He said, ‘No.'”