It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "There is no prayer for the one who has not performed ablution, and there is no ablution for the one who has not mentioned the name of Allah (that is, has not said Bismillah)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 183