Nafi' narrates from Ibn Umar (may Allah be pleased with them both) that whenever the Messenger of Allah (peace and blessings be upon him) intended to perform i'tikaf, his bedding or his cot would be spread out for him beside the Pillar of Repentance, on the side facing the qiblah, and he would lean against it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10284