(a) 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: "When one of you prostrates, he should not kneel down as a camel kneels; rather, he should first place his hands on the ground, then his knees."
(b) In the narration of Abu Dawud: Muhammad bin Abdullah bin al-Hasan informed me that "He should place his hands before his knees."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2633