Answer
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.
In this fatwa:
The phrase “MashaAllah” is commonly used by people when they see something pleasing and delightful from the blessings of Allah, to ward off the evil eye, or to prevent oneself from feeling pride or amazement.
Answering your question, the Fatwa Center at Islam Q and A, states:
The phrase “MashaAllah” is commonly used by people when they see something pleasing and delightful from the blessings of Allah, to ward off the evil eye, or to prevent oneself from feeling pride or amazement.
Allah, the Most High, says: “If only you had said, upon entering your property, ‘This is what Allah has willed! There is no power except with Allah!’ Even though you see me inferior to you in wealth and offspring.” (Al-Kahf, 18:39)
Ibn Kathir (may Allah have mercy on him) commented: “This is an incitement and encouragement to do so. That is, when you were pleased upon entering it and looked at it, you praised Allah for what He bestowed upon you, giving you wealth and children that He did not give to others, and you said, ‘MashaAllah, la quwwata illa billah.'”
For this reason, some of the early Muslims said: “If something about one’s condition, wealth, or children pleases them, they should say, “MashaAllah, la quwwata illa billah,” and this is derived from this noble verse.
Anas (may Allah be pleased with him) reported that that the Prophet Muhammad (peace be upon him) said: “When Allah blesses a servant with a blessing such as good family, wealth, or children, and he says, ‘MashaAllah, la quwwata illa billah,’ he will not see any harm in them other than death. And he used to interpret this verse: If only you had said, upon entering your property, “MashaAllah, la quwwata illa billah”?” (Reported by Abu Ya`la al-Mawsili)
Sheikh Ibn Uthaymeen (may Allah have mercy on him) said:
“So when a person sees something he likes and fears the evil eye, he says, ‘MashaAllah, tabarak Allah,’ so that the one being admired is not afflicted by the evil eye.
Similarly, when someone sees something pleasing in his wealth, he should say, ‘MashaAllah, la quwwata illa billah,’ so that he does not become impressed with himself and boast about this wealth that pleased him. Therefore, when he says, ‘MashaAllah, la quwwata illa billah,’ he has entrusted the matter to its rightful owners, blessed and exalted.”
Read also:
Patience and Thankfulness on the Path to Allah
Tips for Developing Attitude of Gratitude
Thankfulness…Why Is It So Difficult?
Prophet Muhammad: The Thankful Slave
Almighty Allah knows best.
Source: IslamQa.Info