Times Of Karâhat
There are three periods of time during which it is makrûh tahrîmî, i.e. harâm (forbidden), to perform a namâz. If the namâz you start to perform within one of these three periods is (an obligatory prayer termed) fard, it will not be sahîh (valid). If it is (a supererogatory one termed) nâfila, you will have committed an act of (harâm termed) makrûh tahrîmî, although the namâz you perform will be sahîh. Such supererogatory prayers of namâz should be discontinued, and reperformed at some other time. The first of these three periods of time begins as the Sun rises in the morning, and continues for forty (40) minutes. The end of this period is termed the time of dhuhâ or the time of ishrâq. The second period (or time) of karâhat is when the Sun is at culmination, (or zawâl).
And, forty (40) minutes prior to sunset begins the third period of karâhat. Sunrise is the duration of time that begins with the time of tulû', i.e. the time when the upper limb of the Sun emerges on the (visible horizon termed) ufq-i-mer'î, and continues until it ascends to a height at which it is too bright to look at (with the naked eye), i.e. until the time of dhuhâ, which is at the same time the end of the time of karâhat. When we say that the Sun is at culmination (in the Islamic sense) we mean that it is within the celestial circle that circumscribes the region termed the shar'î (Islamic) zawâl. In other words, it is the period of time between the time a period of Tamkin prior to true culmination and the time another periof of Tamkin after it. This period of time begins, say, in Istanbul, twenty (20) minutes before the early afternoon prayer. By 'sunset' we mean the time that starts when the Sun begins turning pale enough to be looked at and continues until it sets. The length of this time varies between thirty-seven minutes and forty minutes at locations on latitude 41 degrees North, such as Istanbul. It averages out at forty minutes. The beginning of this time is called isfirâr-i-shams or time of karâhat. Only the day's late afternoon prayer (and only its fard part) can be performed as the Sun sets. And then it is makrûh tahrîmî to delay the late afternoon prayer until the time of isfirâr. According to Imâm Abû Yûsuf, only on Friday, it is not makrûh tahrîmî to perform a nâfila namâz when the Sun is directly overhead. However, this qawl (narration conveyed on the authority of the great disciple of Imâm a'zam Abû Hanîfa) is (among those narrations termed) da'îf. Other impermissible acts of worship within this period are performing the namâz of janâza for a dead Muslim if the burial preparations were made beforehand, and to perform prostrations called sajda-i-tilâwat and sajda-i-sahw. If the funeral preparations are made within this period, then it is sahîh to perform the namâz of janâza within this period.
There are two periods of time wherein only nâfila prayers of namâz are makrûh to perform. In the morning, no supererogatory namâz, with the exception of the sunnat of (the day's) morning prayer, are performed between the break of dawn and sunrise. Once the day's late afternoon prayer has been performed. it is makrûh tahrîmî to perform a nâfila namâz before evening prayer. After the imâm has mounted the minbar and the muazzin has started saying the iqâmat on Friday, and as the imâm conducts the fard namâz in jamâ'at at other times, it is makrûh to start performing a nâfila namâz, e.g. the time's sunnat. The only sunnat namâz that is not makrûh to start performing in such cases, is the sunnat of morning prayer; and then this prayer should be performed at some distance from the line of worshippers, or behind one of the pillars in the mosque. As it was stated (by some authorized scholars), a sunnat namâz that you started performing before the imâm mounted the minbar should be (continued and) completed.
If the Sun rises as you are performing a morning prayer, the prayer will not be sahîh (valid). If the Sun sets as you are performing an evening prayer, the prayer will be sahîh. If, after performing an evening prayer, you fly west by plane and see the Sun, you will have to reperform the evening prayer after sunset. If the same event takes place (as you are fasting in Ramadân and) and you have broken your fast, you will have to make qadâ by reperforming your fast after the 'Iyd.