It is narrated from Sayyiduna al-Bara' bin Azib (may Allah be pleased with him) that when the Messenger of Allah (peace and blessings be upon him) prostrated, he placed his hands on the ground facing the qiblah; his fingers and palms were also facing the qiblah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2696