Answered by Shaykh Amjad Rasheed
If a latecomer is standing to complete his final rak`ah and another man comes and stands next to him, intending to follow him, what should the latecomer do?
Answer:
السؤال: مسبوق يقوم ويتم الركعة , فجاء رجل حنبه ونوى أن يقتدي به فماذا يفعل المسبوق ؟ الجواب : يجوز للمسبوق في هذه الحالة أن يتمَّ صلاته وحده دون نية الإمامة ، وله أن ينوي إمامة ذلك الرجل فيحوز فضيلة الجماعة .
It is permissible for the latecomer, in this case, to complete his prayer by himself without intending to lead the other person. He may also intend to lead him, because he is allowed to attain the merit of the group prayer.
Amjad Rasheed
[Translated by Sr. Shazia Ahmad]