Sahih al-Bukhari 216
Ablutions (Wudu')
One of the major sins is not to protect oneself (one's clothes and body) from one's urine (i.e., from being soiled with it)
Narrated Ibn `Abbas: Once the Prophet, while passing through one of the graveyards of Medina or Mecca heard the voices of two persons who were being tortured in their graves. The Prophet (ﷺ) said, "These two persons are being tortured not for a major sin (to avoid)." The Prophet (ﷺ) then added, "Yes! (they are being tortured for a major sin). Indeed, one of them never saved himself from being soiled with his urine while the other used to go about with calumnies (to make enmity between friends). The Prophet (ﷺ) then asked for a green leaf of a date-palm tree, broke it into two pieces and put one on each grave. On being asked why he had done so, he replied, "I hope that their torture might be lessened, till these get dried."