The Messenger of Allah ﷺ said, "Whoever is given a religious ruling without knowledge, the sin of it falls upon the one who issued the ruling."
قال رسول الله ﷺ: من أختي بغير علم كان إثمه على من أفتاه.
Abu Dawud (3657) narrated it from Hasan bin Ali, who said, Abu Abdul-Rahman Muqri narrated to us, Saeed - meaning Ibn Abu Ayub - narrated to us, from Bakr bin Amr, from Muslim bin Yasar - Abu Uthman - from Abu Hurairah, and he related the hadith. Its chain is hasan because of Bakr bin Amr, for he is truthful and his hadith is hasan.Ibn Majah (53) narrated it through another route from Muslim bin Yasar, with the same wording.Abu Dawud also narrated it from Sulayman bin Dawud, who said, Ibn Wahb informed us, Yahya bin Ayub narrated to me, from Bakr bin Amr, from Amr bin Abu Nuaymah, from Abu Uthman Tanbudhi (who is Muslim bin Yasar), the foster-brother of Abdul-Malik bin Marwan, who said, I heard Abu Hurairah, and he related something similar. He added in it, "Whoever advises his brother on a matter while knowing that the right course lies elsewhere has betrayed him."This addition is daif because of Amr bin Abu Nuaymah, for he is unknown. Daraqutni said, "An Egyptian, unknown, to be disregarded." Ibn Hibban mentioned him among the trustworthy narrators and said, "He makes mistakes."As for Bakr bin Amr, he narrated from Muslim bin Yasar directly, as Mizzi stated, though it has also been said that he narrated from Amr bin Abu Nuaymah, from him. It appears, then, that the insertion of Amr bin Abu Nuaymah between Bakr bin Amr and Muslim bin Yasar is to be regarded as an addition within an otherwise continuous chain, since Abu Abdul-Rahman Muqri established this chain, and Hakim, following his route, recorded it in Mustadrak (1/126), declaring it sahih according to the standard of the two Shaykhs, and said, "I know of no flaw in it."The early scholars disliked giving religious rulings without knowledge. Abdullah bin Abbas said, "Whoever issues a ruling while being unclear about it, its sin falls upon him." See Madkhal (186).And from Ibn Masud, who said, "Whoever has knowledge should speak according to his knowledge, and whoever does not have knowledge should say, 'Allah knows best,' for Allah said to His Prophet , "Say, I ask of you no payment for it, and I am not one of those who pretend" [Surah Sad 38:86]." See its sourcing in Madkhal (797).And Ibn Mubarak was asked, "When may a man give a religious ruling?" He said, "When he is knowledgeable of the tradition and discerning in his reasoning." Madkhal (187).