Sayyiduna Abu Umamah (may Allah be pleased with him) narrates: Once the Prophet (peace and blessings be upon him) was walking on foot during intense heat when the strap of his sandal broke. A man brought a strap and fitted it to his sandal. Then the Prophet (peace and blessings be upon him) said: "If you knew (the reward of) what you have provided to the Messenger of Allah, you would not consider little what you have provided to the Messenger of Allah."
Ahmad and al-Tabarani recorded it; its chain contains a narrator, Ali bin Yazid al-Alhani, who is da'if (weak).