Reference: Fataawa at-Talaaq – Question 32, Page 57
Question: What is the ruling regarding someone who intended to divorce his wife, and then delayed doing so?
Response: If a man intended to divorce his wife, then left that and did not do anything, then [by this] a divorce is not constituted, as divorce is not constituted by an intention [itself]. [This is] as the Prophet (sal-Allaahu ‘alayhi wa sallam) said:
«Indeed Allaah overlooks the affairs of my ummah, so long as it has not done the act or spoken [about it]».
So long as he did not [verbally] pronounce [the divorce] or write it, rather just intended doing so, then this constitutes nothing, and his wife [therefore] remains under his protection, and no divorce has been constituted until he writes the divorce or [verbally] pronounces it.