Sahih Muslim Book 1, Hadith Number 279.

Chapter : To habituate the heart with Faith which due to its weakness, is scared and the forbiddance to call positively one believer without a definite proof.

The same hadith has been narrated on the authority of Muhammad b Sa’d and these words (are also there): The Messenger of Allah (may peace be upon him) gave a stroke on my neck or between my two shoulders and said: Sa’d, do you fight with me simply because I gave (a share) to a man?