All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
Some jurists are of the view that it is an obligation for whoever has a tattoo to remove it if possible, because tattoos are an obstacle for becoming pure. So according to them, ablution, prayer and the Tawaaf (circumambulation around the Ka'bah) are not valid, in line with the opinion of the majority of the scholars who consider that it is a condition to have ablution and be pure. However, he is not obligated to remove it if one is unable to do so except by experiencing harm, and he is not sinful, provided he repents from it. In such a case, ablution, prayer, Tawaaf and Hajj are all valid for a person who was tattooed before the age of puberty. Some jurists are of the view that it is not an obligation in principle for a young person who has a tattoo to remove it, and his ablution is valid because the tattoo is under the skin and this does not prevent water from reaching it (the skin). To conclude, Hajj is valid for whoever is not able to remove the tattoos.
Saying that a person would go to Hellfire if he has a tattoo is not correct; we have already mentioned that a young person below the age of puberty is not held accountable, and the same thing applies to an insane person. A person who undergoes tattooing as an adult and then regrets and repents, Allaah will accept his repentance. Allaah says (which means): {And it is He who accepts repentance from His servants and pardons misdeeds.}[Qur'an 42:25]. So after one repents, he will not enter Hellfire. For more details please refer to Fataawa: 89503 and 82394.
Allaah knows best.