Sayyiduna Jabir bin Abdullah (may Allah be pleased with them both) said that the Messenger of Allah (peace and blessings be upon him) used to stay at the rear of the caravan; he would urge on the weak, let them ride behind him, and supplicate for them.
(b) It is narrated from Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) that he too used to do the same.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10352