• تَفْشَلَا
• تَفْشَلُوا۟
• فَشِلْتُمْ

Appears 4 times in the Quran.

1. 3:122 إِذْ هَمَّت طَّآئِفَتَانِ مِنكُمْ أَن تَفْشَلَا وَٱللَّهُ وَلِيُّهُمَا وَعَلَى ٱللَّهِ فَلْيَتَوَكَّلِ ٱلْمُؤْمِنُونَ

   When two parties from among you had determined that they should show cowardice, and Allah was the guardian of them both, and in Allah should the believers trust.
   

2. 3:152 وَلَقَدْ صَدَقَكُمُ ٱللَّهُ وَعْدَهُۥٓ إِذْ تَحُسُّونَهُم بِإِذْنِهِۦ حَتَّىٰٓ إِذَا فَشِلْتُمْ وَتَنَٰزَعْتُمْ فِى ٱلْأَمْرِ وَعَصَيْتُم مِّنۢ بَعْدِ مَآ أَرَىٰكُم مَّا تُحِبُّونَ مِنكُم مَّن يُرِيدُ ٱلدُّنْيَا وَمِنكُم مَّن يُرِيدُ ٱلْءَاخِرَةَ ثُمَّ صَرَفَكُمْ عَنْهُمْ لِيَبْتَلِيَكُمْ وَلَقَدْ عَفَا عَنكُمْ وَٱللَّهُ ذُو فَضْلٍ عَلَى ٱلْمُؤْمِنِينَ

   And certainly Allah made good to you His promise when you slew them by His permission, until when you became weak-hearted and disputed about the affair and disobeyed after He had shown you that which you loved; of you were some who desired this world and of you were some who desired the hereafter; then He turned you away from them that He might try you; and He has certainly pardoned you, and Allah is Gracious to the believers.
   

3. 8:43 إِذْ يُرِيكَهُمُ ٱللَّهُ فِى مَنَامِكَ قَلِيلًا وَلَوْ أَرَىٰكَهُمْ كَثِيرًا لَّفَشِلْتُمْ وَلَتَنَٰزَعْتُمْ فِى ٱلْأَمْرِ وَلَٰكِنَّ ٱللَّهَ سَلَّمَ إِنَّهُۥ عَلِيمٌۢ بِذَاتِ ٱلصُّدُورِ

   When Allah showed them to you in your dream as few; and if He had shown them to you as many you would certainly have become weak-hearted and you would have disputed about the matter, but Allah saved (you); surely He is the Knower of what is in the breasts.
   

4. 8:46 وَأَطِيعُوا۟ ٱللَّهَ وَرَسُولَهُۥ وَلَا تَنَٰزَعُوا۟ فَتَفْشَلُوا۟ وَتَذْهَبَ رِيحُكُمْ وَٱصْبِرُوٓا۟ إِنَّ ٱللَّهَ مَعَ ٱلصَّٰبِرِينَ

   And obey Allah and His Messenger and do not quarrel for then you will be weak in hearts and your power will depart, and be patient; surely Allah is with the patient.