Nafi' (may Allah have mercy on him) says: I saw Abdullah bin Umar (may Allah be pleased with them both), when he went to the graves of the martyrs on his she-camel, turn her this way and that. He was asked about it, and he said: I saw the Messenger of Allah (peace and blessings be upon him) on this road on his she-camel, so I said (to myself): Perhaps the foot of my she-camel will fall upon the foot of his (peace and blessings be upon him) she-camel.
[Hasan]
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10301