It’s a great sin to speak about Allah without knowledge about you’re saying and it’s totally forbidden

“Allah has forbidden us to speak about Him without knowledge, and He mentions that alongside shirk and major sins. Allah says (interpretation of the meaning):

“Say (O Muhammad): (But) the things that my Lord has indeed forbidden are Al-Fawahish (great evil sins and every kind of unlawful sexual intercourse) whether committed openly or secretly, sins (of all kinds), unrighteous oppression, joining partners (in worship) with Allah for which He has given no authority, and saying things about Allah of which you have no knowledge.” [al-A’raf 7:33]”

An example of speaking about Allah with no knowledge is saying it is a bid’ah (an innovation) to fast three days (Al-ayyam al-beed) in Sha’ban.”

https://islamqa.info/en/answers/49867/fasting-al-ayyam-al-beed-during-shaban