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How can pious people predict the future?

How are some people whether muslims or non-muslims able to predict certain futuristic events? These people that I am talking about, especially the muslims, are very pious and religious people. If you meet these people and see their lifestyle, they live a very humble and religious life. How can they predict future, specially with some degree of success, when in the Quran Allah clearly states that He alone has the knowledge of the unseen?
One specific verse I would like to mention:
“Allah Alone is the Knower of the Unseen. He never grants the Knowledge of his Ghayb to anyone but to His chosen Messengers and appoints guard before them and behind them.” (Surah Jinn, 72:26-27).”
Also, I understand from Quran that Jinn are able to snatch some information about the future (Surah15 v.17 and 18) and pass it on to the person on the ground. Just the thought of associating a pious person with a jinn does not bode well, at least for the followers of the pious person.
I am also aware of the hadith, the Prophet (PBUH) said: “They (the Jinn) would pass the information back down until it reaches the lips of a magician fortune-teller. Sometimes a meteor would overtake them before they could pass it on. If they passed it on before being struck, they would add to it a hundred lies.” (Al-Bukhari and Tirmidhi). By the way, this pious person that I am speaking about, in the past has successfully predicted some futuristic events.
Again, how can a pious muslim person suggest to a muslim brother that an event (probably a bad event) in the future is going to take place? And what’s happening now is that this muslim brother is taking an action, a drastic step that the entire family disagrees with, to save himself from a bad future that the pious person has had an ilham (inspiration) about.

Answer

When we talk about whether a certain view is correct in religion or not, we have to base our judgment completely on arguments of Quran and hadith. Even if an otherwise impious person presents a sound evidence to support his view, it would be accepted and conversely a view not supported by sound argument even though presented by a very pious person shall not be accepted.
No human is free from Satanic influence in this world. And Satan designs its trap in accordance with an individual’s tastes. For a person inclined towards wealth or women, the design would be different and for the one who has a religious taste it would be different.
In other words, if the question is religious, the answer has to be religious too, no matter who is giving it. And the question whether one should predict the future has been answered by the Quran in the negative.
It is not necessary that an individual realizes that what he is experiencing is Jinn-based. In fact, the cleverness of the Satanic trap causes people who are thus influenced to feel as if “they are guided”. (Quran; 43:37)
What you have mentioned about future events is absolutely correct. Only God knows about them. Nobody has a right to claim that he knows the future. If an individual believes he has guidance about the future which has a chance, even a slight one, of being from Satan, he should be careful enough to not disclose it to anyone. Therefore if an individual is predicting the future and he is not a prophet — and prophets are not going to come anymore — one should not believe in a word of what he says. Instead, one should trust God and do things in accordance with one’s honest understanding.
Your relative would therefore do well to take decision on the matter at hand on the basis of merit. He should consider all the relevant facts before deciding. I would strongly advise him to resort to istikhara. Kindly ask him to see what I have written here: “Procedure and supplication of Istikhara”