Ishaq bin Mansur al-Kausaj إسحاق بن منصور بن بهرام - الكوسج · The Book of Purification

"Whoever performs Wudu' then let him sniff water in the nose and blow it out, and whoever uses small stones (to remove filth) then make it odd (numbered)."

'Where were you, O Abu Hurairah?' He said: 'O Messenger of Allah, you met us but I was Junub, and I did not want to sit in your presence until I had performed Ghusl.' He said: 'Subhan Allah! The believer is not made impure (Najis).'"