(a) It is narrated from Abu Mijlaz (may Allah have mercy on him): I saw Ibn Umar (may Allah be pleased with them both) clip his nails, and I said: "Will you not perform ablution?" He said: "For what should I perform ablution? Do you think yourself cleverer because your family has named you clever?"
(b) It is narrated from al-Sha'bi (may Allah have mercy on him) that he said about a man who clips his nails after ablution: It is (a means of) purification for him.
(c) Al-Hasan (may Allah have mercy on him) said: "There is no ablution for it," and Ata' (may Allah have mercy on him) said: "He should touch it with water." The same is narrated from Ibrahim (may Allah have mercy on him). Al-Zuhri (may Allah have mercy on him) said: "If he wishes he may wipe over it with water, and if he wishes he may leave it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 693