What is the ruling on saying "Ya Din Rabbi" (O Religion of my Lord), and is it considered disbelief (kufr), and is one sinful for merely thinking of it without completing the utterance?

Uttering phrases like "O religion of my Lord, what are you doing?" or "O religion of my Lord, what is wrong with you?" is reprehensible. If the intention behind it is to insult religion, then it is disbelief (kufr). One must avoid such expressions and show reverence for religion, and beware of words of discontent, for "A servant may utter a word that displeases Allah, without giving it any thought, and by it he falls into Hell." The advice is to turn away from obsessive thoughts regarding disbelief and purity, for religion is easy. This is aided by having good assumptions about people and knowing that departing from religion has conditions and impediments that one should refer to scholars for. Among the greatest means is to ask Allah for pardon and well-being (al-afw wal-afiyah), for the Prophet, peace and blessings be upon him, said: "Ask Allah for pardon and well-being, for no one has been given anything better than well-being after certainty (of faith)." The Prophet, peace and blessings be upon him, advised Al-Abbas, may Allah be pleased with him, to ask Allah for well-being in this world and the Hereafter, which indicates its great importance and that it is Allah's defense for the servant against all harm and a bringer of all good.