I have a question. Recently, my house was one of the ones affected by the flood. All of my property and clothing were destroyed. Alhamdulillah, my friends and acquaintances helped, including those who are non-Muslims. They even gave me some of their clothes that they no longer use to help me out. My question is, what is the ruling of me wearing the clothes to pray? The issue is I don’t know whether it has come into najis or not. Hope for an explanation.
Alhamdulillah, praise and gratitude to Allah SWT for His countless blessings for us all. Praise and salutations to our beloved Prophet Muhammad PBUH, his family, companions, and all those who follow his footsteps until the Final day.
We start with the statement of Allah SWT:
“And your clothing purify,” 
AL-Syaukani said the above verse means Allah SWT commanded him to purify his clothing and protect it from najis. While Qatadah said it means to purify yourselves from sins. 
Al-Sa’di in his commentary stated that the possibility that the word ‘clothing’ in this verse means all the actions of Rasullullah PBUH and the meaning ‘purify’ means with sincerity and with the best implementation from any matters that invalidate, damage and decrease the rewards such as shirk, riyak, nifak, ujub, takbur, distracted and others commanded to His slaves to be avoided when worshipping Him. It includes the commandment to clean one’s clothing from najis. The reason is the matter is one of the parts of the perfection of purification especially in prayer, as stated by scholars which state removing najis is included in the valid conditions of prayer.
Furthermore, there is a possibility that the word ‘clothing’ means exactly that, clothing that we know. In other words, Rasullullah PBUH was instructed to clean his clothing from any najis all the time especially during prayer. If the Prophet PBUH was commanded to purify what is evident, then indeed the purification of what can be seen is a part of the purification of the soul. 
Valid conditions of prayer
Among the valid conditions of prayer is one must be free from any najis on his body, clothing and prayer place. It is understood that najis should be cleaned from one’s clothing through the instruction of Rasullullah PBUH to Khaulah bin Yasar. Khaulah asked the Prophet PBUH:
يَا رَسُولَ اللهِ إِنَّهُ لَيْسَ لِي إِلاَّ ثَوْبٌ وَاحِدٌ وَأَنَا أَحِيضُ فِيهِ فَكَيْفَ أَصْنَعُ ؟ قَالَ : إِذَا طَهُرْتِ فَاغْسِلِيهِ، ثُمَّ صَلِّي فِيهِ
“Messenger of Allah, I have only one clothes and I menstruate in it, how should I do? He said: When you are purified, wash it and pray in it. She asked: If the blood is not removed, (then what)? He said: It is enough for you to wash the blood its mark will not do any harm to you.” 
The above hadith shows that the Prophet PBUH asked for the clothing worn for prayer to be cleansed first from any najis.
Likewise, among the valid conditions of prayer is to cover the aurah completely. The aurah for man in prayer is between his navel and knees. Thus, it is obligatory to cover it so that not even a little part of it is seen. As for the woman, it is her whole body except her face and palms. Thus, it is obligatory for the aurah to be covered completely except for other parts. 
Imam al-Nawawi explained that covering the aurah is among the valid conditions of prayer. If any of the aurah part is exposed when he is praying,then the prayer is invalid. Regardless of whether the exposed part is small or big, or for man or woman, prayer performed alone or in congregation, the obligatory or sunnah prayers, funeral prayer, tawaf, tilawah prostration or prostration of gratitude. 
Praying with clothes from non-Muslims
There is a narration from Mughirah bin Syu’bah, where he stated:
أن النبيَّ ﷺ لبس جُبَّةً روميَّةً ضيقةَ الكمين
“The Prophet wore a Byzantine cloak with narrow sleeves.” 
In another narration, it is stated that the cloak with narrow sleeves is from Syria. 
As we know, the Byzantine Empire at the time was Christian. The same for other countries at the time, where they have yet to accept Islam. However, the Prophet PBUH wear their clothes.
Regarding this matter, there is an Islamic legal maxim that states:
الْأَصْلَ فِي الْأَشْيَاءِ الطَّهَارَةُ حَتَّى تَتَحَقَّقَ النَّجَاسَةُ
“The origin of something is it is pure and clean until najis is evident.” 
Furthermore, al-Sa’di also stated the maxim:
والأَصْلُ في مِيَاهِنَا الطهارةُ # والأرضُ والثيابُ والحجارةُ
“The origin of water is pure, The same for soil, clothing and rock.”
Syeikh Hamad Abdullah commented on this maxim saying that the meaning of this maxim is that the origin of water, soil, clothing and rock is pure and clean. In other words, if you have clothing of which you don’t know whether it has come in contact with najis or not. Then, in this matter, you can wear it and pray, even when the clothing is from non-Muslims, for the original ruling for the clothing is that it is clean and pure.
Likewise, for clothing from non-Muslims, they can be used and it is permissible to be worn in prayer as long as we don’t know that it has najis. However, washing it first is better and prioritized – as to avoid any khilaf and this is encouraged. 
According to the above discussion and arguments, in our opinion, it is permissible to wear clothing given by non-Muslims when praying as long as there is no evidence that it has najis and that it covers the aurah completely.
However, if we have the opportunity to wash it first before wearing it, this is better and prioritized.
Hence, we include the supplication to be recited when we are putting on our clothes:
الْحَمْدُ لِلَّهِ الَّذِي كَسَانِي هَذَا الثَّوْبَ وَرَزَقَنِيهِ مِنْ غَيْرِ حَوْلٍ مِنِّي، وَلَا قُوَّةٍ
“Praise is to Allah Who has clothed me with this (garment) and provided it for me, though I was powerless myself and incapable.” 
May Allah SWT grant us a clear understanding in religion. Ameen.
 See Zubdah al-Tafasir min Fath al-Qadir, by Sulaiman al-Asyqar, pg. 776
 See Tafsir al-Sa‘di, 1/895
 Narrated by Abu Daud (365)
 See al-Fiqh al-Manhaji, 1/124
 See al-Majmu‘ Syarh al-Muhazzab, 3/172
 Narrated by al-Tirmizi (1768)
 Narrated by al-Bukhari (363) and Muslim (274)
 See Tarh al-Tathrib fi Syarh al-Taqrib, 2/114
 See Syarh Manzumah al-Qawaid al-Fiqhiyyah li al-Sa‘di, 3/3
 Narrated by Abu Daud (4023)