It is reported about Sayyidah Maymunah bint Sa'd (may Allah be pleased with her) that she said: O Messenger of Allah! Tell us the ruling: what causes the punishment of the grave? The Prophet (peace and blessings be upon him) said: The traces of urine (that is, its splashes). If urine gets on anyone, he should wash that place, and if he does not find water, he should wipe it with pure earth.
Al-Tabarani recorded it in al-Mu'jam al-Kabir, and its chain consists of narrators who range between da'if (weak) and majhul (unknown).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الطهارة / 1035