مِشْكَاةُ الْمَصَابِيحِ
Mishkat al-Masabih 489
Purification
Laws about different kinds of water - Section 3
وَعَنْ عُمَرَ بْنِ الْخَطَّابِ رَضِيَ اللَّهُ عَنْهُ قَالَ: لَا تَغْتَسِلُوا بِالْمَاءِ الْمُشَمَّسِ فَإِنَّهُ يُورِثُ البرص. رَوَاهُ الدَّارَقُطْنِيّ
‘Umar b. al-Khattab said, “Do not wash in water which has been exposed to the sun, for it produces leprosy.” Daraqutni transmitted it.
Mishkat al-Masabih, 489ضَعِيفٌ (الألباني)