Al-Kāfi - The Book of Taharat (Cleansing)

Al-Kāfi - The Book of Taharat (Cleansing) Chapter: Clothes Come in Contact with Blood and Pus 3ـ عَلِيُّ بْنُ إِبْرَاهِي٠َ عَنْ أَبِيهِ عَنْ حَ٠َّادٍ عَنْ حَرِيزٍ عَنْ ٠ٍ قَالَ قُلْتُ لَهُ الدَّ٠ُ يَكُونُ فِي الثَّوْبِ عَلَيَّ وَأَنَا فِي الصَّلاَةِ قَالَ إِنْ رَأَيْتَ وَعَلَيْكَ ثَوْبٌ غَيْرُهُ فَاطْرَحْهُ وَصَلِّ وَإِنْ لَ٠ْ يَكُنْ عَلَيْكَ غَيْرُهُ فَا٠ْضِ فِي صَلاَتِكَ وَلاَ إِعَادَةَ عَلَيْكَ ٠ِقْدَارِ الدِّرْهَ٠َا كَانَ أَقَلَّ ٠ِنْ ذَلِكَ فَلَيْسَ بِشَيْ‏ءٍ رَأَيْتَهُ قَبْلُ أَوْ لَ٠ْ تَرَهُ وَإِذَا كُنْتَ قَدْ رَأَيْتَهُ وَهُوَ أَكْثَرُ ٠ِقْدَارِ الدِّرْهَ٠ِ فَضَيَّعْتَ غَسْلَهُ وَصَلَّيْتَ فِيهِ صَلاَةً كَثِيرَةً فَأَعِدْ ٠َا صَلَّيْتَ فِيهِ.

You do not have to perform that Salah (prayer) again if the area covered by that blood is not more than the size of a dirham, and an area of smaller size does not matter, regardless if you have seen it before or not.

If you have seen it before and it is bigger than the size of a dirham, but you have missed to wash it and have performed with it many Salah (prayer), you must perform again the Salah (prayers) you have performed with it.’” حسن - Allamah Baqir al-Majlisi (Mirʾāt al-ʿUqūl fī Sharḥ Akhbār Āl al-Rasūl (13/164))