Sayyiduna al-Zubayr (may Allah be pleased with him) narrates: I saw the Messenger of Allah (peace and blessings be upon him) when he went to climb onto the rock. At that time he (peace and blessings be upon him) was wearing two coats of mail. He (peace and blessings be upon him) could not climb onto the rock, so Sayyiduna Talhah bin Ubaydullah (may Allah be pleased with him) sat down beneath him. Then he (peace and blessings be upon him) climbed up onto the rock, and the Messenger of Allah (peace and blessings be upon him) said: "Talhah has made it obligatory," meaning Paradise.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 17932