How are we to understand the meaning of the verse: "Ask not about things which, if made plain to you, may cause you trouble"? And does this include not asking about matters of worship?

The noble verse: "O you who have believed, do not ask about things which, if made manifest to you, would trouble you" (Al-Ma'idah: 101), prohibits asking about matters from which there is no benefit, and whose clarification might lead to harm or sadness for the questioner. It is not a prohibition against a Muslim asking about what he needs in his worship.

Ibn Kathir said: "This is an admonition from Allah to the believers against asking about things that are of no benefit to them, for their manifestation might displease them." Al-Sa'di said: The verse prohibits asking about things which, if clarified, would cause distress and sadness, such as some Companions asking about their fathers, or asking about hypothetical matters, or questions that lead to legal strictures, or asking about what does not concern one. As for questions that do not result in such outcomes, they are commanded, as in His (Allah's) saying: "So ask the people of the message if you do not know."

The excessive questioning that is prohibited in the Hadith (definition): "And He disliked for you three things: gossiping, asking too many questions, and wasting money" refers to excessive questioning in jurisprudential matters out of pedantry and artificiality concerning what has not been revealed, and seeking difficult questions and hypothetical cases. The Salaf (pious predecessors) disliked that and considered it a burden.