Allah, the Blessed and Exalted, says: "Then when they fall (lifeless) on their sides." [Surah al-Hajj: 36]
Imam Mujahid (may Allah have mercy on him) says: "(It means) when they fall to the ground."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / Q10213