Dieser Beitrag ist zwar schon älter, aber für die Leute, die es nicht wissen (und bitte macht die Recherche): Tattoos sind laut folgendem Hadith/Überlieferung haram:

عن عبد الله بن مسعود رضي الله عنه أن النبي صلى الله عليه وسلم: "لعن الواشمات والمستوشمات، والنامصات والمتنمصات، والمتفلجات للحسن المغيرات خلق الله تعالى."

Abdullah ibn Mas'ud reported that Allah's Messenger (ﷺ) cursed those women who engage in tattooing and those who have themselves tattooed, along with those who pluck hair from their faces and create spaces between their teeth for beautification, altering what Allah has created (Muslim). This underlines the severity of such actions and their contradiction to the natural order created by Allah (https://en.islamonweb.net/islamic-perspectives-on-tattoos-and-piercings)

Es werden manchmal weiter Hadithe diesbezüglich erwähnt. Aber darüber hinaus ist eine weitere Sache noch viel verwerflicher an deinem Vorhaben: sich das Wort Allah bzw. Alhamdulillah zu tätowieren ist total unangebracht, da du dich als Mensch an unreinen Plätzen aufhalten wirst wie z.B. Toilette, vielleicht Club usw.

„Ibn Qudaamah (may Allah have mercy on him) said in al-Mughni (1/109): If he wants to enter the washroom and has something with him on which the name of Allah is mentioned, it is mustahabb for him to put it down or take it off. If he keeps with him the thing that he has on which the name of Allah is mentioned, and takes care not to drop it, or turns the part of the ring on which it is written to face his palm, there is nothing wrong with that. Ahmad said: If the ring has the name of Allah on it, he should turn it to face his palm and enter the washroom. This was the view of Ishaaq and Ibn al-Musayyab, and al-Hasan and Ibn Sireen granted concessions allowing that. End quote. Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked: What is the ruling on entering the washroom with papers on which the name of Allah is mentioned? He replied: It is permissible to enter the washroom with papers on which the name of Allah is mentioned, so long as they are in a pocket and are not out in the open; rather they are hidden and covered. End quote. 

Fataawa min al-Tahaarah, p. 109“

(https://islamqa.info/amp/en/answers/121141)