Question: If a safari (traveler) performs four rak'ats instead of two rak'ats deliberately or forgetfully, what should he/she do? If a safari imam performs four rak'ats instead of two rak'ats by mistake, does it affect the salat of a muqim (resident) following him?
If a safari (traveler) offers four rak'ats instead of two, the last two rak'ats are considered nafila (voluntary). He/she is sinful because he/she disobeyed the order, because he/she has omitted the takbir of iftitah for a nafila salat, because he/she has omitted the salam of the fard salat, and because he/she has mixed the nafila salat with the fard salat. However, if he/she performs four rak'ats forgetfully, he/she must do sajda as-sahw at the end of salat.
If a safari imam offers four rak'ats instead of two rak'ats by mistake, the salat of a muqim following him is nullified. If the safari does not sit in the second rak'at, his/her fard salat will not be valid. If he/she stands up for the third rak'at by mistake and at that time intends to stay for 15 days in the place he/she is a traveler, he/she must perform that salat as four rak'ats. However, he/she must repeat the qiyam and ruku' of the third rak'at, for he/she did these two as nafila (voluntary). An act of worship done as nafilah does not replace a fard act of worship.
A safari should say short surahs in salat and should not say tasbihat less than three times. He/she may omit sunnat salats except the sunnat salat of Salat al-Fajr. It is permissible to omit sunnat salats due to a valid excuse if his/her journey involves hardship. Similarly, during travel, it is permissible, too, to delay Salat al-Isha until the time when it is makruh to perform it.
Question: If a safari offers four rak'ats instead of two when performing Salat az-Zuhr, Salat al-Asr, or Salat al-Isha, does he/she have to make it up if he/she realizes his/her mistake later?
No, he/she does not have to make it up.