It is narrated from Hazrat Nafi that Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) used to pray in the mosque of Dhul-Hulaifah, then he would come out and mount (his ride), and at that time he would enter into the state of Ihram.
Hadith Referenceموطا امام مالك رواية يحييٰ / كتاب الحج / 736