The Prophet (peace and blessings be upon him) said:
"Indeed, Allah Almighty is Witr (One) and loves what is odd, so when you perform istinja (using clods or stones), use an odd number."
Hadith Referenceصحیح الجامع الصغیر / حرف الألف / 1830
Hadith Gradingالألبانی:صحيح
Hadith Takhrij[ع] عن ابن مسعود. مجمع الزوائد ١/٢١١١.