Praise be to Allah, and may peace and blessings be upon the Messenger of Allah. To proceed:
The basic principle for a Muslim is to think well of others. It is not permissible to accuse another Muslim or think badly of them based merely on suspicion or obsessive doubts. The Prophet ﷺ said:
“Beware of suspicion, for suspicion is the falsest of speech.”
When is it permissible to refrain from eating food?
If it is merely a suspicion or an obsessive doubt without any evidence, it should not be given attention. Rather, a Muslim should think well of his fellow Muslim.
However, if there are strong indications or a reasonable likelihood of genuine harm, there is nothing wrong with taking precautions and refraining from eating the food, because Islamic law seeks to preserve life and prevent harm.
Does refusing food indicate weakness of certainty?
Refusing food because of obsessive doubts and baseless suspicions may result from weakness of certainty and following the whispers of Satan. However, refraining from it because of a valid reason or clear indications of harm is part of taking permissible precautions and does not contradict reliance upon Allah.
What did the Prophet ﷺ do with the poisoned sheep?
It is authentically reported that the Prophet ﷺ initially ate from it because he did not know that it was poisoned. When he was informed of this, he ordered those present to stop eating and did not continue eating from it. This demonstrates the permissibility of avoiding food when its harmful nature becomes known.
Conclusion
The basic principle is to think well of Muslims and not pay attention to obsessive doubts. If there is no evidence or reliable indication, one should not think badly of others or refuse food merely because of suspicion. However, if there is a reasonable likelihood of genuine harm, it is permissible to refrain from eating it while relying upon Allah and taking appropriate precautions.
And Allah knows best.