Hadith 1:123
and Al-Hakim reported that:
“Urination is the main cause of punishment in the grave”. [Its chain of narrators is authentic].
وَلِلْحَاكِمِ: { أَكْثَرُ عَذَابِ اَلْقَبْرِ مِنْ اَلْبَوْلِ } وَهُوَ صَحِيحُ اَلْإِسْنَاد ِ (123)
Original Reference: Bulugh al-Maram 104