Abu Hurayrah and Abu Sa‘īd al-Khudri (may Allah be pleased with both of them) reported that the Prophet (may Allah's peace and blessings be upon him) said that Allah affirms what His slave says. If one says, "there is no god but Allah, and Allah is Greatest," Allah says: "Indeed, there is no god but Me, and I am Greatest." When one says, "Allah is Greatest, and there is no might nor power save with Allah," Allah would affirm it. So, if a person said this Dhikr (There is no god but Allah, and there is no might nor power save with Allah) then died, the Fire would not consume him, i.e. that would be a reason not to be burnt in Hellfire. Therefore, every Muslim should memorize this Dhikr and say it when he is ill, so that Allah would grant him a good end for his life, Allah, the Almighty, Willing.