It was reported in the press that they agreed to it:
Hamas will ‘accept PA governing Gaza’ under ceasefire deal
17 Feb 2025
https://www.thejc.com/news/israel/hamas-accept-pa-governing-gaza-ceasefire-rch26gjt
It was also not Hamas’ idea but the mediators including the US and UAE:
UAE in talks with US, Israel about provisional government for post-war Gaza
7 Jan 2025
https://m.jpost.com/middle-east/article-836444
the Palestinian Authority agreed to it as well
*Palestinian Authority 'Ready to Take Full Responsibility for Gaza Strip,' Despite Not Being Party to Cease-fire Agreement
18 Jan 2025
https://www.haaretz.com/israel-news/2025-01-18/ty-article/.premium/palestinian-authority-ready-to-take-full-responsibility-for-gaza-strip/00000194-79cc-dce1-a396-fded13bb0000
Wiki summarises the phase 3 oversight as follows
”Third stage
In this stage, Hamas would have released all the remains of deceased Israeli captives, in exchange for Israel releasing the remains of deceased Palestinian bodies that it holds.[158] Israel would end the blockade of the Gaza Strip and Hamas would not rebuild its military capabilities.[15]
Supervision and guarantors
Initially, it was proposed that activities in the Gaza Strip would be supervised by Egypt, Qatar, and the United Nations,[158] who along with the United States would guarantee the proposal and its provisions. As of February 2025, the government of Israel continued to insist that in its implementation of the "second-phase" (see supra) of the peace deal, the Gaza Strip must be de-militarized and that the Palestinian Authority (PA) was in no position to govern the Gaza Strip.[159]”
As seen above, Hamas & everyone else had agreed to it, so it would have happened if Israel had chosen to move on to phase 2 and then phase 3…but instead they chose to re-start the war
“On the early morning of 18 March 2025, during Ramadan, Israel conducted a surprise offensive of "extensive" airstrikes on Gaza, thereby shattering the almost two-month truce.[408][43] Israeli forces acknowledged that they were "conducting extensive strikes", and separately stated that their attack "plan was kept in closed circles in the IDF to create an element of surprise and deception."[409][410]…..”
Israeli journalist Barak Ravid argued that while journalists described the resumption of airstrikes as being a result of a "collapse", the ceasefire was deliberately collapsed by the Israeli government itself:
https://news.walla.co.il/item/3735371