Answer
✅Answer: Please pay attention to the following narrations:
1 مُحَمَّدُ بْنُ عَلِيِّ بْنِ الْحُسَيْنِ بِإِسْنَادِهِ عَنْ زُرَارَةَ قَالَ: قُلْتُ لِأَبِي جَعْفَرٍ أَ لَا تُخْبِرُنِي مِنْ أَيْنَ عَلِمْتَ وَ قُلْتَ أَنَّ الْمَسْحَ بِبَعْضِ الرَّأْسِ وَ بَعْضِ الرِّجْلَيْنِ فَضَحِكَ فَقَالَ يَا زُرَارَةُ قَالَهُ رَسُولُ اللَّهِ وَ نَزَلَ بِهِ الْكِتَابُ مِنَ اللَّهِ عَزَّ وَ جَلَّ لِأَنَّ اللَّهَ عَزَّ وَ جَلَّ قَالَ فَاغْسِلُوا وُجُوهَكُمْ فَعَرَفْنَا أَنَّ الْوَجْهَ كُلَّهُ يَنْبَغِي أَنْ يُغْسَلَ ثُمَّ قَالَ وَ أَيْدِيَكُمْ إِلَى الْمَرافِقِ فَوَصَلَ الْيَدَيْنِ إِلَى الْمِرْفَقَيْنِ بِالْوَجْهِ فَعَرَفْنَا أَنَّهُ يَنْبَغِي لَهُمَا أَنْ يُغْسَلَا إِلَى الْمِرْفَقَيْنِ
📚Al-Faqih, Vol. 1, p. 103-212
Translation: Imam Baqir (peace be upon him) said in a hadith: '...Indeed, Allah, the Mighty and Exalted, says: 'So wash your faces,' so from here we knew that the entire face is deserving of being washed. Then Allah says: 'And your hands up to the elbows,' so He connected and joined the two hands up to the elbows, so we knew that the two hands up to the elbows are washed (completely).'
2 عَنْ عُثْمَانَ بْنِ عِيسَى عَنْ سَمَاعَةَ عَنْ أَبِي عَبْدِ اللَّهِ قَالَ: مَنْ نَسِيَ مَسْحَ رَأْسِهِ أَوْ قَدَمَيْهِ أَوْ شَيْئاً مِنَ الْوُضُوءِ الَّذِي ذَكَرَهُ اللَّهُ تَعَالَى فِي الْقُرْآنِ- كَانَ عَلَيْهِ إِعَادَةُ الْوُضُوءِ وَ الصَّلَاةِ.
📚Al-Tahdhib, Vol. 1, p. 102
Translation: Imam Sadiq (peace be upon him) said: 'Whoever forgets the wiping of the head or the wiping of his two feet or anything from the 'wudu' that Allah the Exalted mentioned in the Qur'an, it is on him to repeat the 'wudu' and the prayer.'
3 عَنْ زُرَارَةَ عَنْ أَبِي جَعْفَرٍ أَنَّهُ قَالَ:
لَا تُعَادُ الصَّلَاةُ إِلَّا مِنْ خَمْسَةٍ الطَّهُورِ وَ الْوَقْتِ وَ الْقِبْلَةِ وَ الرُّكُوعِ وَ السُّجُودِ.
📚Al-Faqih, Vol. 1, p. 339
Translation: Imam Baqir (peace be upon him) said: 'Prayer is not repeated except for five things: purity ('wudu' and 'ghusl' and 'tayammum') and time and 'qibla' and 'ruku'' and 'sujud'.'
✅From the few above narrations, it is clear that the face and hands must be washed completely for 'wudu', and if a person realizes after 'wudu' or after prayer that water did not reach a part of his hand or face and there was a barrier on it, he has not performed a part of the 'wudu' that Allah mentioned in the Qur'an, and according to the second and third narrations, he is obligated to repeat his 'wudu' and prayer (meaning he must perform 'wudu' again and pray).
Forgetting a part of 'wudu'
Repeating prayer