What is the ruling on saying: "Had it not been for my diligence, I would not have succeeded in the exam"? And is it permissible to say "had it not been for so-and-so" if the reason is genuinely valid in Islamic law or by observation, or must one say "had it not been for Allah and then so-and-so"?

It is permissible to attribute a thing to its cause if the speaker believes that the cause does not act on its own except by the will of Allah, and that Allah is the true Bestower of blessings. This attribution becomes forbidden, and may even reach the level of polytheism (shirk), if one believes that the cause acts on its own, or forgets Allah's favor, or does so out of arrogance. The Holy Quran states that every blessing is from Allah. As for the saying: "Were it not for Allah, then so-and-so," it is permissible, and "Were it not for so-and-so" is permissible if it is not accompanied by a corrupt belief. The best and most complete in monotheism is to say: "Were it not for Allah alone." Therefore, the saying: "Were it not for my diligence, I would not have succeeded," is permissible if it is intended that diligence is merely a cause and that the favor is from Allah. It is better to say: "Were it not for Allah's grace." It is forbidden if it is intended for self-aggrandizement and attributing the favor to oneself.