Answer
Wa `alaykum as-Salamu wa Rahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Dear brother, thank you for your question that shows your interest in Islam.
We should differentiate between bad omens and practical scientific predictions based on considerations and logical assumptions, while pessimism is simply a negative attitude.
Responding to your question, Dr. Yusuf `Ali At-Tarif, Professor at Imam Muhammad bin Su`ud Islamic University, states:
Bad omens stem from the belief that certain things one sees or hears are to be taken as signs that something bad is going to happen. Omens are irrational. They are not to be confused with practical scientific predictions based on considerations of natural cause and effect that Allah has placed in creation.
Rather, an omen is a superstition. It is a superstition that is often connected with embarking upon some enterprise or journey, and the “sign” that appears makes the superstitious person refrain from undertaking it. The pagans of Mecca saw bad omens in certain birds.
Prophet Muhammad (peace and blessings be upon him) said, “There are no such things as omens.” (Al-Bukhari)
He also said, “Omens are polytheism.” (Abu Dawud)
Such superstitions are sinful, and belief in them is forbidden by Islam. Only Allah Almighty determines what will befall in the future, not the stars, flights of birds or any other arbitrary happening that has no observable cause and effect relationship with the matter at hand.
Pessimism, on the other hand, is simply a negative attitude. It is the prevalence of belief that the outcome will not be as one desires it to be or will not meet with one’s expectations. All of us experience this at one time or another. At times, there may be rather sensible reasons for feeling this way. For instance, a student might be pessimistic about test results after taking a difficult test where the questions appeared confusing (or even before taking a difficult test the student did not properly prepare for).
This is merely a natural fear of a bad outcome – nothing more nothing less. Such pessimism does not compromise our faith in Allah and His power unless it causes us to entertain negative thoughts about Allah. Under all circumstances, we must believe that Allah has power over the outcome and that what He wills must come to pass. If He wills, He can prevent the bad outcome.
A Muslim believes that everything that takes place in the universe occurs according to Allah’s will and decree. Whatever befalls us would not have passed us by, and whatever we miss in our lives would not have been for us. This is something we should remind ourselves of whenever the gloominess of our circumstances gives us a sense of fear or foreboding.
We should turn our hearts to Allah and remind ourselves that His decree will prevail. Our fears will not prevent a bad outcome from taking place, if that is what Allah has decreed. This will steady our hearts and encourage us to beseech Allah more often in prayer, for He is indeed Almighty and Most-Merciful.
Allah Almighty knows best.
Excerpted, with slight modification, from: en.islamtoday.net