Regarding the subject of Shortening and Combining Prayer, Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, who stated:
1) There is general consensus among scholars that if a traveling person is determined to return as soon as his work is done and does not know when that will be, then he may continue to pray Qasr as long as he is on travel.
If, however, a person decides to settle down in a city, the moment he does so, he ceases to be a traveler, and, therefore, he must pray full.
If, on the other hand, one is determined to stay only for a few days the number of which he knows precisely, then he should pray full, according to a great number of scholars, if his stay exceeds more than four days. The Hanafi School, however, puts the number of allowable days at fifteen, while a third group of scholars put it at eighteen.
The first view seems to be the safest view to follow, as it has been based on the Prophet’s practice. According to authentic reports, he stayed in Makkah for four days, and during his stay he prayed Qasr; he had already known in advance how many days he would be staying. He is reported to have prayed Qasr for eighteen and twenty days on two different occasions, when, most likely, he had no idea as regards the number of days he would be staying.
having said this, I should rush to state that if anyone follows the position of the Hanafi School, he should not be blamed for his action, for theirs is a Fiqh- ruling based on acceptable practices of the Salaf as-Salih (pious predecessors). Since it is merely a question of differences of interpretation based on valid Ijtihad (creative exercise of reasoning), one should never make a big issue out of such differences of opinion among Imams.
2) The most accurate way to count the number of days for a traveler is to consider oneself a Musaafir (traveler) only after one has crossed the boundaries of his city of residence. Thus in case of people living in Toronto, if they are in a long distance journey they will be considered travelers only after they have crossed the boundaries of GTA. The days of stay are calculated by excluding the day/days of going and returning.
3) Yes, according to vast majority of scholars and Imams, it is perfectly allowed for a traveler to combine Zuhr and `Asr, and Maghrib and `Isha. This ruling (known as Jam`) is based on the authentic traditions which clearly state that the Prophet, peace and blessings be upon him, had combined Zuhr and `Asr as well as Maghrib and `Isha on a number of occasions while traveling.
According to Hanafi School, however, combining prayers is allowed only during Hajj while performing the rite of standing in `Arafah. At other times they allow only what is often termed as Jam suwari (a kind of combining): By this they mean to say that you are allowed, for instance, to delay Zuhr and pray it at the last time of Zuhr and then pray `Asr at the first time of `Asr.
The majority view allowing combining of prayers as mentioned earlier has been considered to be the most authentic; it has been adopted later by many scholars belonging to Hanafi School as well.
4) While combining prayers, you are allowed to make either taqdim (advancing) or ta’khir (delaying): In other words, you are allowed to advance the second prayer to the time of the first prayer. Thus, if you are combining Zuhr and `Asr, you can first pray Zuhr at the time of Zuhr, and then advance `Asr by praying immediately, or if you wish you can defer praying Zuhr until the time of `Asr arrives, in which case, you will first pray Zuhr and then pray `Asr afterwards. The same procedure applies to combining Maghrib and `Isha as well.
An important word of caution concerning Jam` is that there is no combining of Fajr with Zuhr, or `Asr with Maghrib, or ‘Isha with Fajr.
It is also worth mentioning that while praying Qasr during travel is highly recommended—some Imams such as Abu Hanifah even consider it as obligatory—during travel, praying Jam’ is only allowed while one is actually traveling or pre-occupied with pressing circumstances. Jam’ is rare, while Qasr is common.
a final remark to be made is that if a person is aimlessly wandering, he is not considered a traveler and is, therefore, not allowed to make use of the allowances of Qasr and Jam`(Shortening and Combining Prayer).
As for the nawafil prayers, Shaykh Ibn ‘Uthaymeen said:
With regard to the regular Sunnah prayers, I have studied what was narrated in the Sunnah concerning the nafil prayers, and it seems to me that the regular Sunnah prayers of Zuhr, Maghrib and `Isha’ should not be offered (by the traveler). But he may offer other nafil prayers apart from that, such as the Sunnah of Fajr, the Sunnah of Witr, qiyaam al-layl, Duha and tahiyyat al-masjid (two rak’ahs to greet the mosque), and nafil prayers in general.