Sayyiduna Abu Hurairah (may Allah be pleased with him) and Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) narrate this statement of the Noble Prophet (peace and blessings be upon him): "Whoever performs ablution should put water into his nose, and whoever uses stones (for cleaning) should do so an odd number of times." (Imam Ibn Hibban, may Allah have mercy on him, says:) The word "istinshar" means to expel water from the nose, and "istinsaq" means to draw water into the nose. The statement of the Noble Prophet (peace and blessings be upon him), "Whoever performs ablution should do istinshar," means that he should do istinsaq. Thus, the Noble Prophet (peace and blessings be upon him) here used the initial word "istinsaq" for the concluding act, which is "istinshar," because istinshar only occurs when it is preceded by istinsaq. And "istijmar" means to attain purity, that is, to remove impurity from both exits.
Hadith Referenceصحیح ابن حبان / كتاب الطهارة / 1438
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - «صحيح أبي داود» (128): ق.فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح على شرط مسلم