Mujahid (may Allah have mercy on him) says: Whoever recites it as "sawafin" says (it means): "It is tied," and whoever recites it as "sawaff", (it means): "Lined up in front." [Sahih. Recorded by al-Tabari in his Tafsir: 9/152]
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10218