Answered by: Maulana Mohammed Kamran Abid
When I first properly started practicing Islam properly whilst being baligh, I did not think it was necessary to use tissue after urinating. This means that I did not perform istibra to free myself of the remaining leftovers of urine and I was very ignorant and there were a few times which I let other people in salah. My question is: Do I need to repeat those salahs? Do the people who I led behind me need to repeat those salahs too? This was a few years ago. I am a male.
In the name of Allah, the Most Gracious, the Most Merciful
Istibra the action of waiting for urine drops until a person is certain and content that all the drops of urine have come out. Istibra is necessary and wudu would not be correct if Istibra is not done completely.
Therefore, if you are sure nothing exited the urethra when you began your wudu, then you don’t have to repeat your Salah, however, if you think urine drop continued after or at the time of wudu, then you would have to repeat your Salah and notify the specific people who were behind you to repeat that specific Salah. If you don’t know exactly who prayed behind you, then you can put a note regarding the specific Salah that needs to be repeated.
Only Allah knows best
Written by Maulana Mohammed Kamran Abid
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
 (قَوْلُهُ: يَجِبُ الِاسْتِبْرَاءُ إلَخْ) …
هُوَ طَلَبُ الْبَرَاءَةِ مِنْ الْخَارِجِ بِشَيْءٍ مِمَّا ذَكَرَهُ الشَّارِحُ حَتَّى يَسْتَيْقِنَ بِزَوَالِ الْأَثَرِ
… أَمَّا نَفْسُ الِاسْتِبْرَاءِ حَتَّى يَطْمَئِنَّ قَلْبُهُ بِزَوَالِ الرَّشْحِ فَهُوَ فَرْضٌ وَهُوَ الْمُرَادُ بِالْوُجُوبِ، وَلِذَا قَالَ الشُّرُنْبُلَالِيُّ: يَلْزَمُ الرَّجُلَ الِاسْتِبْرَاءُ حَتَّى يَزُولَ أَثَرُ الْبَوْلِ وَيَطْمَئِنَّ قَلْبُهُ. وَقَالَ: عَبَّرْت بِاللُّزُومِ لِكَوْنِهِ أَقْوَى مِنْ الْوَاجِبِ؛ لِأَنَّ هَذَا يُفَوِّتُ الْجَوَازَ لِفَوْتِهِ فَلَا يَصِحُّ لَهُ الشُّرُوعُ فِي الْوُضُوءِ حَتَّى يَطْمَئِنَّ بِزَوَالِ الرَّشْحِ. اهـ.
(رد المحتار على الدر المختار, vol. 1, pg. 344, دار الفكر-بيروت)