What is the definition of "rizq" (provision), and does it increase and decrease, or is it predestined for a person and all they have to do is strive? And do acts of disobedience and obedience affect its increase or decrease?

Sustenance (rizq) is what Allah bestows upon His servant, be it wealth or other things. It is predetermined and decreed; it neither increases nor decreases in the knowledge of Allah Almighty. Divine decree (qadaa') is of two types: an absolute, eternal decree that does not change, and a suspended (or conditional) decree, which is what is recorded in the scriptures of the angels and can change through supplication (du'a) and charity (sadaqah). The servant must strive to earn sustenance, for abandoning the means (asbab) is a disparagement of the Sacred Law. As for sins, it has been narrated that they impede sustenance, even though some huffadh (hadith preservers) have weakened the wording. Conversely, acts of obedience and good deeds bring blessings to one's lifespan and increase sustenance, as Allah Almighty says: "And if they had remained on the straight path, We would have given them abundant water" (Quran 72:16), and His saying: "And if only the people of the cities had believed and feared Allah, We would surely have opened to them blessings from the heaven and the earth" (Quran 7:96).