Peace be upon you. According to Grand Ayatollah Sayyid Sistani (may Allah protect him): Ritual impurity (janabah) occurs only through sexual intercourse or the discharge of semen. Therefore, merely dreaming without the discharge of semen does not necessitate a bath. If you are certain that a fluid has exited and you are sure it is semen, then you must perform the bath. If you are not sure it is semen: If you feel the sensation of ejaculation, desire, and bodily relaxation upon the discharge of the fluid, you can conclude that it is semen, and you must perform the bath. If these three characteristics are not present, then you do not need to perform the bath. This applies unless the person is ill and may not feel the ejaculation; in that case, the mere feeling of desire is sufficient. According to Grand Ayatollah Sayyid Khamenei (may Allah protect him): The same ruling applies. If you doubt whether any fluid has exited or not, then there is no obligation upon you. Source: Sayyid Sistani: Minhaj al-Salihin – Part One, Issues 169, 183. Sayyid Khamenei: Easy Jurisprudential Rulings: Bath Issues 143, 146.