قال النبي صلّى الله عليه وسلم: كل مسكر خمر وكل خمر حرام.رواه مسلم
The Prophet ﷺ said:
Every intoxicant is Khamr and ALL Khamr is Haraam (STRICKLY FORBIDEN). [Collected by Muslim]
Imaam San’aanee (rahimahullah) said in his book Subulus Salaam which is the explanation of Bulughul Maraam,
Verily all things that causes intoxication is Haraam (strictly forbidden) even if it is not ingested by drinking it like Marijuana (for example).
Imaam Ath-Thahabee (rahimahullah) said in his book entitled Al Kabaa’ir,
Manufactured Marijuana from the Cannabis plant is Haraam (strictly forbidden) like Alcohol and the one who ingests it is to receive the same legal punishment as the one who drinks Alcohol. In fact Marijuana, is more despicable than Alcohol.
Shaikhul Islaam Ibn Taymiyyah (rahimahullah) mentioned in his Fataawa when he was questioned about the ruling of ingesting Marijuana,
Marijuana is a vile solid substance which is Haraam (strictly forbidden) whether one becomes high from it or not. To become intoxicated or high from it is Haraam (strictly forbidden) by consensus of the Scholars (of Islam). Consequently, the one who deems and declares it Halaal (permissible) or thinks it is Halaal (permissible) is to be encouraged to repent, (if they repent good) but if not, they are to be killed as apostates (who have left Islam and are no longer Muslims). They are not to be prayed over nor buried in the Muslim cemetery.
Imaam Ibn Hajar said in his book entitled Az-Zawaajir,
Al Quraafee (rahimahullah) who was from the Imaams of the Maalikee Mathab mentioned, “Ibn Tayymiyyah (rahimahullah) stated there is a consensus on the prohibition of Marijuana and that the one who considers it permissible has committed disbelief and left Islam.