We set out with the Messenger of Allah (may Allah's peace and blessings be upon him) on a military campaign. We were six men and had one camel with us which we would take turns riding it. So our feet were injured (from the long walk) and my feet were injured

Hadīth explanation: Abu Mūsa (may Allah be pleased with him) and some of his companions went on a military expedition with the Prophet (may Allah's peace and blessings be upon him). They were six men and had only one camel that they would take turns riding it, until they reached their destination. Their feet got injured from walking for a long distance through the desert, to the extent that Abu Mūsa's toenails fell off.

They did not have anything to cover their feet with because their sandals were torn on the way, so they were walking barefoot. Hence, their feet were terribly injured but they still kept walking to meet the enemy. They would wrap rags around their feet, which proves that their footwear was ruined from walking so far on a rugged terrain. This was one of the reasons for naming this expedition: the battle of Dhāt Ar-Riqā‘.

Abu Mūsa reported this Hadīth but later regretted having mentioned it because he disliked to disclose any of his good deeds. This means that Abu Mūsa after mentioning this Hadīth wished that he had never mentioned it, because of what it implies of self praise, and because hiding good deeds from others is recommended, unless the benefit for revealing the deeds outweighs concealing it, such as if it is performed by someone who is an example for others.

A relevant Hadīth in this regard reads: "So he concealed giving out charity so much that his left hand does not know what his right hand gives out." [Al-Bukhāri and Muslim]