The Islamic State (ISIS) is Sunni; Soleimani was Shi’ite. Hamas is Sunni as well, but receives funding from Iran.
In any case, apostasy is a death penalty offense in Islamic law, so this is a serious charge. It’s based on the Qur’an: “They wish you would disbelieve as they disbelieved so you would be alike. So do not take from among them allies until they emigrate for the cause of Allah. But if they turn away, then seize them and kill them wherever you find them and take not from among them any ally or helper.” (Qur’an 4:89)
A hadith depicts Muhammad saying: “Whoever changed his Islamic religion, then kill him” (Bukhari 9.84.57). The death penalty for apostasy is part of Islamic law according to all the schools of Islamic jurisprudence.
This is still the position of all the schools of Islamic jurisprudence, both Sunni and Shi’ite. Sheikh Yusuf al-Qaradawi, the most renowned and prominent Muslim cleric in the world, has stated: “The Muslim jurists are unanimous that apostates must be punished, yet they differ as to determining the kind of punishment to be inflicted upon them. The majority of them, including the four main schools of jurisprudence (Hanafi, Maliki, Shafi’i, and Hanbali) as well as the other four schools of jurisprudence (the four Shiite schools of Az-Zaidiyyah, Al-Ithna-‘ashriyyah, Al-Ja’fariyyah, and Az-Zaheriyyah) agree that apostates must be executed.”
Qaradawi also once famously said: “If they had gotten rid of the apostasy punishment, Islam wouldn’t exist today.”
“ISIS: Hamas ‘apostate’ for calling Soleimani a ‘martyr,’” JNS, January 7, 2021 (thanks to The Religion of Peace):
Islamic State (ISIS) weekly Al Naba ran an editorial on Jan. 1 criticizing fellow Sunni terror group Hamas for calling slain Shi’ite Iranian Gen. Qassem Soleimani a “martyr,” according to the Middle East Media Research Institute’s Jihad and Terrorism Threat Monitor (MEMRI-JTTM).
The article, titled “When Netanyahu becomes Syria’s martyr,” begins by calling Hamas “apostate” for describing Iran and its allies who “kill Muslims in other countries, rape their women, destroy the homes over their heads and force hundreds of thousands of youths to disappear in prisons” as martyrs and jihadis.
The article asks how Hamas would react if Syrian factions were to declare Israeli Prime Minister Benjamin Netanyahu a “Syrian martyr,” and accuses the Gaza-based terror group of lauding Iran because it provides them with money and weapons….