Is the default state of things permissibility or prohibition if there is no religious text commanding or forbidding something?

The fundamental principle concerning acts of worship is that they are prohibited unless sanctioned by Islamic law, whereas the fundamental principle regarding matters other than worship is permissibility until there is evidence of prohibition. Ibn Uthaymeen clarified this, saying: "And the fundamental principle concerning things is permissibility, but prohibit an act of worship unless sanctioned by the Lawgiver."

Explanation of this principle: The fundamental principle concerning things (objects, benefits, transactions, and actions) is permissibility, based on Allah's saying: "It is He who created for you all of that which is on the earth," and His saying: "O you who have believed, fulfill [all] contracts." As for acts of worship, the fundamental principle concerning them is prohibition unless Allah permits it, based on His saying: "Or have they partners who legislated for them of religion what Allah has not authorized?" and the Prophet, peace and blessings be upon him, said: "Whoever introduces into this matter of ours something that does not belong to it will have it rejected."

Based on this, if an action is an act of worship and the Prophet, peace and blessings be upon him, did not perform it, then one must refrain from it unless there is evidence for its legality. However, if it is not an act of worship, the fundamental principle is its permissibility unless there is evidence of its prohibition.

There is no harm in offering condolences at the grave, whereas sacrificing at graves is absolutely impermissible, even if for the purpose of charity, due to the potential for exaggeration, and Shaykh al-Islam Ibn Taymiyyah prohibited it.