عَنْ عَلِيٍّ رَضِيَ اللَّهُ عَنْهُ قَالَ: إِنَّ مِنَ السُّنَّةِ فِي الصَّلَاةِ وَضْعَ الْأَكُفِّ عَلَى الْأَكُفِّ تَحْتَ السُّرَّةِ
Sayyiduna Ali (may Allah be pleased with him) says that placing the palms of the hands over each other below the navel in prayer is Sunnah.