What is the ruling on one who curses and says, "Cursed be the one who knocked you," and is this considered disbelief if the intent is to curse the Creator, and is the one who says it excused if he is ignorant of the meaning?

The meaning of the mentioned curse (la'n) is unclear, and a ruling on it cannot be made without knowing the speaker's intention. Whoever utters it while ignorant of its meaning does not become an unbeliever by it, even if the curse itself is an act of disbelief (kufr) or disobedience (ma'siyah). This is based on the saying of Ibn Qasim: "One who narrates an act of disbelief they heard, without believing in it, does not become an unbeliever... Similarly, one who utters a word of disbelief without knowing its meaning [does not become an unbeliever]." It is obligatory to guard the tongue from cursing and reviling, based on the Prophet's (peace be upon him) saying: "Whoever believes in Allah and the Last Day, let him speak good or remain silent," and his saying: "The believer is not one who slanders, or curses, or speaks obscenities, or is foul-mouthed."