Abu Dawud Book 19, Hadith Number 3649.

Chapter : Precaution in giving legal decisions.

Narated By Abu Hurairah : The Prophet (PBUH) said: If anyone is given a legal decision ignorantly, the sin rests on the one who gave it. Sulayman al-Mahri added in his version: If anyone advises his brother, knowing that guidance lies in another direction, he has deceived him. These are the wordings of Sulayman.