Sayyiduna Ibn Umar (may Allah be pleased with them both) said that the Messenger of Allah (peace and blessings be upon him) said: "Whoever performs ablution and mentions the name of Allah over his ablution, that is, says 'Bismillah', this ablution will be (complete) purification for his body; and whoever performs ablution but does not mention the name of Allah, that is, does not say 'Bismillah', this ablution will be purification only for his limbs."
(b) This narration too is weak, like the previous narration.
(c) Abu Bakr al-Dahiri is untrustworthy according to the scholars of hadith.
(d) This narration has also been reported from Sayyiduna Abu Hurayrah (may Allah be pleased with him) as marfu' (attributed to the Prophet) through a weak chain.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 199