ʿĀd Denied the Messengers

What was their response? Allah (swt) says:

Qālū yā Hūdu mā jiʾtanā bi-bayyinatin wa mā naḥnu bi-tārikī ālihatinā ʿan qawlik, wa mā naḥnu laka bi-muʾminīn. They said: O Hūd, no evidence have you brought us, and we shall not leave our gods for your mere saying, and we are not believers in you. They rejected.

Allah (swt) says: kadhdhabat ʿĀdun al-mursalīn — ʿĀd denied the messengers. How many messengers did they receive? One. But Allah (swt) said: kadhdhabat ʿĀdun al-mursalīn. The people of ʿĀd have disbelieved in the messengers — plural, not one. But they only received one messenger. How come it's made plural? If you refuse one messenger, it is as if you refused them all, because all of the messengers came with the same message. So if you refuse the message of Hūd, it is as if you refused the message of everyone. If you refuse the message of Muhammad (peace be upon him), it would not suffice you to believe in ʿĪsā, or Mūsā, or any other Nabī. If you disbelieve in one Nabī, in one Rasūl, it is as if you have disbelieved in all of them.

So even — let's assume, even, that today there's somebody who believes in ʿĪsā and Mūsā, and believes in Allah only, and doesn't believe in any other god; but he does not believe in Muhammad (peace be upon him): that is not Islam. You have to believe in all of the Anbiyāʾ of Allah (swt), from Ādam until Muhammad (peace be upon him). So they disbelieved in Hūd only; but Allah (swt) said kadhdhabat ʿĀdun al-mursalīn: they disbelieved in all of the messengers.