It is narrated from Sayyiduna Jabir (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: When any one of you performs istinja with stones, he should use an odd number of stones.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 15296
Hadith Gradingحکم دارالسلام:حديث صحيح، وهذا إسناد قوي كسابقه