In the first place, we would like to stress that Salah (ritual Prayer) is a religious duty that has specified times. Allah says: “Verily, the prayer is enjoined on the believers at fixed hours.” (An-Nisa’: 103)
These fixed hours have come to be recognized by following the actual practice of the Prophet (peace and blessings be upon him). So, each of the five Prayers has its own time limit that should not be violated, whether by doing the Salah ahead of time—which is prohibited and categorically unacceptable—or by exceeding the time limit and performing the Salah late. Unless there is an acceptable excuse, one commits a sin by so doing.
Sheikh Muhammad Nur Abdullah, President of ISNA and member of the Fiqh Council of North America, states the following: “When it comes to combining Salah, there is a Hadith in which it reported that the Prophet (peace and blessings be upon him) combined Zhuhr with `Asr, and Maghrib with `Isha’, and it was not raining, and he was not traveling or sick. And when asked about the reason, Ibn `Abbas (may Allah be pleased with him) responded that he (peace and blessings be upon him) “did not want to put hardship for his Ummah.”
This Hadith is evidence for the scholars who say that it is allowed to combine Zhuhr and `Asr if there is a need or necessity, or if someone if afraid to miss the time of `Asr, especially in the winter when the time is very short for `Asr.
So, my opinion is that we can take this rukhsah or legal concession and apply it if there is a need, for example if someone is attending classes, or a doctor is doing an operation, or for any similar need.
However, I caution you not to make this a habit, because a Prophetic Hadith tells us: The best action most liked by the Prophet was to pray on time.
So, if you go out (for shopping, for example) in winter, and you are afraid you will come back after the time of `Asr, then you can combine Zhuhr and `Asr, but not on every day so that it won’t be a habit.”
Having clarified the above, we would like to furnish you with the following relevant decision taken by the European Council for Fatwa and Research:
“The Prophet (peace and blessings be upon him) is reported to have combined Zhuhr with `Asr Prayers and Maghrib with `Isha’ Prayers when he was not in a state of danger and when there was no rain. Ibn `Abbas (may Allah be pleased with him) was asked: Why did he do so? He replied: He wanted to lift the difficulty from upon his Ummah.”
Thus, it is permitted for a Muslim to combine Zhuhr and `Asr Prayers in European [and other high latitude] countries during winter when the day is very short and it becomes increasingly difficult for employees to pray each in its own time. The Council, however, warns Muslims against combining the said Prayers without the actual need to and against making this permission a constant habit.”