Allah commands Dhikr after finishing the Fear prayer, in particular, even though such Dhikr is encouraged after finishing other types of prayer in general. In the case of Fear prayer, Dhikr is encouraged even more because the pillars of the prayer are diminished since they move about while performing it, etc., unlike other prayers. Allah said about the Sacred Months,

﴿فَلاَ تَظْلِمُواْ فِيهِنَّ أَنفُسَكُمْ﴾

(so wrong not yourselves therein), even though injustice is prohibited all year long. However, injustice is particularly outlawed during the Sacred Months due to their sanctity and honor. So Allah's statement,

﴿فَإِذَا قَضَيْتُمُ الصَّلَوةَ فَاذْكُرُواْ اللَّهَ قِيَـماً وَقُعُوداً وَعَلَى جُنُوبِكُمْ﴾

(When you have finished Salah, remember Allah standing, sitting down, and on your sides,) means, in all conditions,

﴿فَإِذَا اطْمَأْنَنتُمْ فَأَقِيمُواْ الصَّلَوةَ﴾

(But when you are free from danger perform the Salah.) when you are safe, tranquil and fear subsides,

﴿فَأَقِيمُواْ الصَّلَوةَ﴾

(perform the Salah) by performing it as you were commanded; fulfilling its obligations, with humbleness, completing the bowing and prostration positions etc. Allah's statement,

﴿إِنَّ الصَّلَوةَ كَانَتْ عَلَى الْمُؤْمِنِينَ كِتَـباً مَّوْقُوتاً﴾

(Verily, the Salah is Kitaban on the believers at fixed hours.) means, enjoined, as Ibn `Abbas stated. Ibn `Abbas also said, "The prayer has a fixed time, just as the case with Hajj.'' Similar is reported from Mujahid, Salim bin `Abdullah, `Ali bin Al-Husayn, Muhammad bin `Ali, Al-Hasan, Muqatil. As-Suddi and `Atiyah Al-`Awfi.