Bulugh al-Maram

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 ِ 1‏ .‏