Hadith: The Messenger of Allah (may Allah's peace and blessings be upon him) wore two coats of mail. He tried to rise over a boulder, but he could not. Then Talhah bowed down and lifted the Prophet, so he could settle on the boulder. He then heard the Prophet saying: It is obligatory for Talhah

عن الزُّبير بن العَوَّام رضي الله عنه قال: كان على النبي صلى الله عليه وسلم دِرْعان يوم أحد، فنهض إلى الصَّخرة فلم يستطع، فأَقعد طلحة تحته، فصعد النبي -صلى الله عليه وسلم عليه- حتى استوى على الصخرة، فقال: سمعتُ النبي صلى الله عليه وسلم يقول: «أَوْجِبْ طلحة».
[حسن] - [رواه الترمذي وأحمد]

Az-Zubayr ibn al-‘Awwām (may Allah be pleased with him) reported that on the Day of (the battle of) Uhud, the Messenger of Allah (may Allah's peace and blessings be upon him) wore two coats of mail. He tried to rise over a boulder, but he could not. Then Talhah bowed down and lifted the Prophet, so he could settle on the boulder. He (Az-Zubayr) then heard the Prophet (may Allah's peace and blessings be upon him) saying: "It (Paradise) is obligatory for Talhah."
Hasan/Sound. - [At-Tirmidhi]

Explanation

The Prophet (may Allah's peace and blessings be upon him) was wearing two coats of iron mail to protect himself from the enemies' stabbings in the battle of Uhud. Then, he turned towards a boulder to climb on it, but he could not. So Talhah (may Allah be pleased with him) came and sat under the Prophet (may Allah's peace and blessings be upon him) helping him climb and settle over the boulder. Upon this, the Prophet (may Allah's peace and blessings be upon him) said: "It (Paradise) is obligatory for Talhah", It means that Talhah guaranteed himself Paradise by what he had done on this day, and he deserves it.