What is incumbent upon one who prayed Asr three rak'ahs and remembered the deficiency after the time for Maghrib had begun, whether or not he had become engaged in worldly matters and spoken about them?

If a worshipper says the tasleem before completing their prayer out of forgetfulness, then remembers immediately after the tasleem or a short time later, they must complete the remaining part of the prayer, and their prayer is valid. It is also sunnah for them to perform the prostration of forgetfulness (sujud al-sahw). However, if a long time passes customarily, or if they speak for a purpose unrelated to the prayer, their prayer becomes null and they must repeat it.

Some scholars are of the view that the prayer is not invalidated by speaking after the tasleem if it was due to forgetfulness, whether the speech was for the benefit of the prayer or otherwise, because the worshipper did not intentionally make a mistake. Nevertheless, it is safer to repeat the prayer to avoid scholarly disagreement. However, if the worshipper is doubtful about the completeness of their prayer after finishing it, they should not pay attention to this doubt.