The command to use an odd number of stones refers to an odd number that is more than one, such as three or more (for example, five, seven, etc.), because sometimes the term "odd" is also applied to one. However, using only one stone for istinja is not sufficient, because the Prophet (peace be upon him) commanded that less than three stones should not be considered sufficient for istinja.
Sayyiduna Jabir (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "When any one of you uses stones for istinja (cleaning after relieving oneself), he should use three stones."
Hadith Takhrij«صحيح مسلم: كتاب الطهارة: باب الايتار فى الاستنثار والاستحمار: 239 ، مسند احمد: 400/3 ، والبيهقي: 507 ، من طريق أبى الزبير عن جابر: وابن شيبه: 134/1»