Muhammad is reported to have said that one who eats 7 Ajwa dates will be immune from magic and poison on the day that he eats them:
Sahih al-Bukhari 5445
Narrated Sa`d:
Allah's Messenger (ﷺ) said, "He who eats seven 'Ajwa dates every morning, will not be affected by poison or magic on the day he eats them."
This is also narrated in Sahih al-Bukhari 5768-69, 5779, Sahih Muslim 2047a-b, and Sunan Abi Dawud 3876.
At best, this statement is dangerously misleading. The most one could say is "Ajwa dates protect against some kinds of poisoning", if that were even true, which would need to be proven. One study by a university in Medina, Saudi Arabia, attempting to vindicate this claim, used Ajwa date extract to treat poisoning brought on by taking too much pain medication. However, the amount of extract that could be obtained from 7 Ajwa dates is very low - much lower than what was used in the study (2 grams of extract per kilogram of bodyweight). And, in the study, the group treated with the extract still sustained damage compared to the control group.
However, there are many types of poisons which would be deadly or harmful regardless of how many Ajwa dates one consumed that morning - even if they took more than 7. This is demonstrated by the fact that hospitals do not keep Ajwa date extract on hand for instances of poisoning. The variable nature of poisoning also ensures that there is no cure-all which will make someone "immune from poison" for a full day, as Muhammad claimed. If there were, it would have a scientific mechanism of action. No such universal mechanism of action to prevent all poisons is possible, and certainly is not present in the ingredients contained within 7 Ajwa dates.
As for the spiritual claim that 7 Ajwa dates protects one from magic for a full day - such a thing cannot be tested, and so is beyond the scope of this article.
Muhammad is also reported to have said that black cumin, or "black seed", contains healing for all diseases except death itself:
Sahih al-Bukhari 5688
Narrated Abu Huraira:
I heard Allah's Messenger (ﷺ) saying, "There is healing in black cumin for all diseases except death."
This is also narrated in Sahih al-Bukhari 5687, Sunan Ibn Majah 3447-49, Jami at-Tirmidhi 2041, 2070.
One could say that this is hyperbole. However, given the subject matter, using hyperbole here seems reckless. There are much safer ways to express this, such as omitting "except death", which seems to explicitly include all non-fatal illnesses.
Obviously, there are innumerable illnesses and diseases which will not be healed by a person consuming black cumin. Yet, taken at face value, this narration seems to promise that healing, or state it as a matter of fact.
Muhammad's statements regarding Ajwa dates and black cumin are reckless, and mostly false. They are at best, misleading overstatements, which will cause harm via perhaps causing someone to forego pursuing real treatment, in favor of merely consuming the remedies recommended by Muhammad.