What should a man do who habitually forgets the 'Isha prayer, and when he prays the four rak'ahs, he says the tasleem after the second rak'ah and glorifies Allah, then stands for the shaf' and witr prayers?

The prayer of one who inadvertently omits a rak'ah (unit of prayer) or a rukn (pillar) becomes invalid if a long period passes before performing it. This length of time is considered long by exiting the mosque or by the passage of a period of time that is customarily deemed long. However, one who frequently experiences forgetfulness is not obligated to perform the prostration of forgetfulness (sujud (definition) al-sahw) due to hardship. Furthermore, it is obligatory for a man to perform prayer in congregation in the mosque.