Before every prayer a Muslim washes the face, hands and feet and wipes over the head. The washing is called wuḍūʾ. In January in Iceland, coming in from a blizzard in winter boots and woollen socks, it is something other than on a warm summer’s day. But the sources speak to that too.
The verse
The instructions, and the reason after them.
يَـٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوٓاْ إِذَا قُمۡتُمۡ إِلَى ٱلصَّلَوٰةِ فَٱغۡسِلُواْ وُجُوهَكُمۡ وَأَيۡدِيَكُمۡ إِلَى ٱلۡمَرَافِقِ وَٱمۡسَحُواْ بِرُءُوسِكُمۡ وَأَرۡجُلَكُمۡ إِلَى ٱلۡكَعۡبَيۡنِۚ وَإِن كُنتُمۡ جُنُبٗا فَٱطَّهَّرُواْۚ وَإِن كُنتُم مَّرۡضَىٰٓ أَوۡ عَلَىٰ سَفَرٍ أَوۡ جَآءَ أَحَدٞ مِّنكُم مِّنَ ٱلۡغَآئِطِ أَوۡ لَٰمَسۡتُمُ ٱلنِّسَآءَ فَلَمۡ تَجِدُواْ مَآءٗ فَتَيَمَّمُواْ صَعِيدٗا طَيِّبٗا فَٱمۡسَحُواْ بِوُجُوهِكُمۡ وَأَيۡدِيكُم مِّنۡهُۚ مَا يُرِيدُ ٱللَّهُ لِيَجۡعَلَ عَلَيۡكُم مِّنۡ حَرَجٖ وَلَٰكِن يُرِيدُ لِيُطَهِّرَكُمۡ وَلِيُتِمَّ نِعۡمَتَهُۥ عَلَيۡكُمۡ لَعَلَّكُمۡ تَشۡكُرُونَ
O you who have believed, when you rise to [perform] prayer, wash your faces and your forearms to the elbows and wipe over your heads and wash your feet to the ankles. And if you are in a state of janabah, then purify yourselves. But if you are ill or on a journey or one of you comes from the place of relieving himself or you have contacted women and do not find water, then seek clean earth and wipe over your faces and hands with it. Allah does not intend to make difficulty for you, but He intends to purify you and complete His favor upon you that you may be grateful
The verse says what to wash, and at the end why: God does not intend to make difficulty for you. That holds for the cold as well.
Cold water
Completing the washing when it is hard is counted especially.
أَلاَ أَدُلُّكُمْ عَلَى مَا يَمْحُو اللَّهُ بِهِ الْخَطَايَا وَيَرْفَعُ بِهِ الدَّرَجَاتِ. قَالُوا بَلَى يَا رَسُولَ اللَّهِ. قَالَ إِسْبَاغُ الْوُضُوءِ عَلَى الْمَكَارِهِ وَكَثْرَةُ الْخُطَا إِلَى الْمَسَاجِدِ وَانْتِظَارُ الصَّلاَةِ بَعْدَ الصَّلاَةِ فَذَلِكُمُ الرِّبَاطُ
“Shall I not point you to that by which God wipes out sins and raises ranks? They said: Yes, Messenger of God. He said: Completing the ablution well despite hardship, taking many steps to the mosque, and waiting for the next prayer after the prayer. That is the ribāṭ, the standing guard.”
Isbāgh al-wuḍūʾ ʿalā l-makārih: washing thoroughly even when it is unpleasant. Scholars have given cold water on a cold day as the first example. Using icy water is not required. In Iceland hot water comes from every tap, and that is perfectly fine. But when you wash in the cold, by a mountain stream or on a journey, it is not for nothing.
Over the boots
Wiping over your footwear instead of taking it off.
The Prophet ﷺ was on a journey, and al-Mughīra ibn Shuʿba went to pull off his leather boots (khuff) so he could wash his feet. He said:
دَعْهُمَا، فَإِنِّي أَدْخَلْتُهُمَا طَاهِرَتَيْنِ
“Leave them, for I put them on when they were clean.”
And he wiped over them with a wet hand. The condition is that you put the footwear on after a full ablution. The time is limited too:
جَعَلَ رَسُولُ اللَّهِ صلى الله عليه وسلم ثَلاَثَةَ أَيَّامٍ وَلَيَالِيَهُنَّ لِلْمُسَافِرِ وَيَوْمًا وَلَيْلَةً لِلْمُقِيمِ
“The Messenger of God ﷺ set three days and nights for the traveller, and a day and a night for the resident.”
All the schools agree on leather shoes and boots that cover the ankle. Socks (jawrab), such as thick woollen socks, are disputed. There is a hadith that the Prophet ﷺ wiped over socks (Sunan Abi Dawud 159), but scholars grade it differently, and the schools set different conditions on thickness and material. If in doubt, ask your imam.
When water is dangerous
On the campaign to Dhāt as-Salāsil, on a cold night, ʿAmr ibn al-ʿĀṣ needed to bathe before the prayer but feared the cold would kill him. So he purified himself with earth (tayammum) and led his companions in the dawn prayer. When the Prophet ﷺ heard of it, he asked:
يَا عَمْرُو صَلَّيْتَ بِأَصْحَابِكَ وَأَنْتَ جُنُبٌ
“ʿAmr, did you lead your companions in prayer while you were impure?”
ʿAmr told him about the cold and quoted the Qur’an: Do not kill yourselves; God is merciful to you (4:29). The Prophet ﷺ laughed and said nothing, and scholars have taken his silence as approval. When water or cold is a real danger to health, tayammum takes the place of washing, as the verse above says. In Iceland this mostly applies on journeys and in the outdoors, not at home where the hot water runs.