Is Saying Good Luck Prohibited?
Question

Is it permissible to say “good luck” or “bad luck”?
Praise be to Allah.Is saying good luck prohibited?
 “Luck” (Hadh) means a share of goodness (or good fortune). Al-Azhari (may Allah have mercy on him) said:
Al-Layth said: “Luck” means a share of blessings or goodness. (Tahdhib Al-Lughah, 3/273)
Ibn Faris (may Allah have mercy on him) said:
“Luck” means a share of good fortune… One who has a share of provision may be described as lucky.” (Majmal Al-Lughah, p. 215)
This is the basic meaning: luck refers to a share of good fortune. The word may also be used to refer to fortune in general, whether it is good or bad. This is how it is used by most people.
Al-Fayruzabadi (may Allah have mercy on him) said:
“Luck” refers to one’s share or fortune; or it may be used specifically to refer to one’s share of good fortune.” (Al-Qamus Al-Muhit, p. 695)
Al-Munawi (may Allah have mercy on him) said:
“Luck” is one’s decreed share.” (At-Tawqif, p. 142)
Based on that, when people say “good luck” and the like, as a kind of supplication for the person to whom it is said, and wishing him well, there is nothing wrong with that, as is obvious; in fact it is praiseworthy because it is a kind of supplication for good and wishing the Muslims well.
But one should not wish or pray for bad luck for a Muslim, because this involves transgression and enmity towards one’s brother in faith.
Muslim narrated (2735) from Abu Hurayrah, from the Prophet (blessings and peace of Allah be upon him) that he said: “A person will still be answered so long as his supplication does not involve sin or severing ties of kinship, and so long as he does not become impatient.” It was said: O Messenger of Allah, what does being impatient mean? He said: “Saying, I offered supplication, and I offered supplication, and I did not receive any response, then he becomes frustrated and stops offering supplication.”
Al-Bukhari (13) and Muslim (45) narrated from Anas ibn Malik that the Prophet (blessings and peace of Allah be upon him) said: “No one of you truly believes until he loves for his brother what he loves for himself.”
Can you say `good luck’ by way of telling something that happened?
If the one who says “good luck” is saying it by way of telling something that happened, so if something good happens to him he says that it was good luck, and if something bad happens to him, he says that it was bad luck, in this case too there does not seem to be anything wrong with it, in sha Allah.
In the case of something good happening, then the matter is clear, and it comes under the heading of speaking of the blessings of Allah and thanking Him for what He decreed for him. 
In the case of something bad happening, then what appears to be the case is that there is also nothing wrong with it, if he is telling of something that actually happened as it appears to be, to the best of the person’s knowledge. It is well-known that things may happen to a person in his life that upset him, and this is bad luck, according to what people customarily think and say; in fact it is something that is also said in the shar`i texts. Allah, may He be Exalted, says (interpretation of the meaning):
“Say (O Muhammad (blessings and peace of Allah be upon him)): I possess no power of benefit or hurt to myself except as Allah wills. If I had the knowledge of the Ghayb (unseen), I should have secured for myself an abundance of wealth, and no evil should have touched me” [Al-A`raf 7:188]
“Is not He (better than your gods) Who responds to the distressed one, when he calls Him, and Who removes the evil, and makes you inheritors of the earth, generations after generations. Is there any Ilah (god) with Allah? Little is that you remember!” [An-Naml 27:62].
This is also what is meant by Hasanah (good, good fortune) and Sayyi’ah (evil, bad fortune), which is referred to in verses such as the following (interpretation of the meaning):
“And if some good reaches them, they say, `This is from Allah,’ but if some evil befalls them, they say, `This is from you (O Muhammad (blessings and peace of Allah be upon him)).’ Say: `All things are from Allah,’ so what is wrong with these people that they fail to understand any word?” [An-Nisa’ 4:78]
“And We tried them with good (blessings) and evil (calamities) in order that they might turn (to Allah’s Obedience).” [Al-A`raf 7:168]
And there are many similar, well known verses.
But in that case it is stipulated that there should be nothing in his words that reflects discontent with what Allah has willed and decreed for him, or thinking negatively of Allah, or attributing the evil or bad fortune to Him, may He be glorified. Bad things, evil and harm are a reality in Allah’s creation and are something that He has decreed will reach His slave according to what is decreed for that person. As for Allah’s will and decree concerning His slaves, it is all good and nothing evil or bad can be attributed to Him, for Allah is exalted and far above all faults and shortcomings.
Can you say ‘good luck’ or ‘bad luck’ thinking that some such thing has happened outside the decree of Allah?
Some people may say “good luck” or “bad luck”, thinking that some such thing has happened outside of the decree of Allah, may He be exalted, or because he thinks that it is connected to some things that have nothing to do with events that happen, such as attributing that to the stars, or some numbers, or some days of the week, and the like.
So if someone says that some person’s good luck or bad luck is due to such a reason, then what he says is wrong and is prohibited, because coincidence with such things, or otherwise, is not something that Allah has made to be the cause of good or evil.
Something similar was indicated in a Fatwa of the Standing Committee, when they were asked:
We often hear that a person has good luck or bad luck (or he is lucky or unlucky). To what extent is it permissible – or not – to believe in luck?
They replied:
“We are required to believe in the will and decree of Allah, so we should be patient in bearing misfortune and we should give thanks to Allah and praise Him for good fortune. We should believe that Allah has divided provision among His slaves, and has decreed that their life spans and deeds should vary, when they were still foetuses in their mothers’ wombs. Allah is most wise in all that He wills and decrees, and every Muslim must attribute what befalls people of blessings and abundant provision to Allah, may He be glorified, Who bestows that and enables people to attain it; and he should attribute anything else that befalls him to the will and decree of Allah. This comes under the heading of attaining sound belief in Tawhid Ar-Rububiyyah (Oneness of divine Lordship). The Muslim must keep away from anything that may undermine his belief and Tawhid, so he should not attribute good and blessings, or calamities and disasters, to luck or stars, for that is not permissible. And Allah is the source of strength. May Allah send blessings and peace upon our Prophet Muhammad and his family and companions.” (Standing Committee for Academic Research and Issuing Fatwas, Shaykh `Abd Al-`Aziz ibn `Abdullah Al Ash-Shaykh, Shaykh `Abdullah ibn Ghadyan, Shaykh Salih Al-Fawzan, Shaykh Bakr Abu Zayd- Fatawa Al-Lajnah Ad-Da’imah, 26/328)
Thinking positively of Allah 
The Muslim should always think positively of Allah, may He be Exalted, concerning whatever befalls him in all his affairs. He may think that he has bad luck in something that may be entirely good for him. So it is better to avoid the phrase “bad luck” in all circumstances. Allah, may He be exalted, says (interpretation of the meaning):
“and it may be that you dislike a thing which is good for you and that you like a thing which is bad for you. Allah knows but you do not know.” [Al-Baqarah 2:216]
Muslim narrated (2999) that Suhayb (may Allah be pleased with him) said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “How wonderful is the situation of the believer, for all his affairs are good. If something good happens to him, he gives thanks for it and that is good for him; if something bad happens to him, he bears it with patience, and that is good for him.”
For more details, please see the following answers: 27192 , 33844 , 46985 , 33842 , 97221 , 2039 , and 158980 .
And Allah knows best.