What is the ruling on one who says "Alhamdulillah" or "Alhamdulillah" instead of "Alhamdu Lillah," and what are the consequences for the speaker and listener of this phrase?

The phrase mentioned is a clear grammatical error. Its speaker intends to say "All praise is due to Allah" (Alhamdulillah) or "All praise is due to Him" (Al-hamdu Lahu). The speaker is not judged as being impious, disobedient, an innovator, or an infidel; rather, the correct way is explained to him.