(Explanation summarized from dorar.net)
The Companions of the Messenger of Allah (peace be upon him) are the best of this Ummah after our Prophet Muhammad (peace be upon him). Despite their virtues, status, and Jihad, they were humans who were susceptible to error, forgetfulness, and sometimes doing things they shouldn’t have done. However, they distinguished themselves by being the quickest to repent and respond to Allah’s and His Messenger’s command.
Buraydah bin Al-Husayb Al-Aslami (may Allah be pleased with him) narrated that he was in an army with Khalid bin Al-Walid (may Allah be pleased with him). The Prophet (peace be upon him) sent Ali bin Abi Talib (may Allah be pleased with him) to Khalid bin Al-Walid to collect the Khums (one-fifth) of the booty from the people of Yemen’s wealth.
Buraydah (may Allah be pleased with him) disliked Ali (may Allah be pleased with him) due to some issues. He saw Ali taking a bath and assumed he had done so after having sexual relations with a slave girl he had chosen for himself from the booty before it was distributed or without ensuring she was free from pregnancy. Buraydah held this against him (and so disliked Ali at that instant).
The response to this was that the Messenger of Allah (peace be upon him) had sent Ali to distribute the booty and collect the khums (one fifth of the total booty), which he did. The slave girl was part of his share, so he (Ali) dealt with her as he pleased.
Regarding Ali’s bath, it was said that perhaps the slave girl was pre-pubescent, and they do not require purification. Alternatively, perhaps he bathed for another reason and did not have any sexual relations with the slave girl, leading to the assumption that his bath was due to sexual relations.
Buraydah’s dislike for Ali due to this incident is excusable, as humans often dislike others when they misunderstand their actions.
When Buraydah reported this to the Prophet (peace be upon him), he asked, “Do you dislike Ali?” Buraydah admitted his dislike, thinking Ali had taken something not rightfully his. The Prophet forbade him from disliking Ali, stating that Ali had more right to the Khums than what he took.
Afterward, Buraydah said, as recorded in Ahmad’s Musnad, “From then on, no one was dearer to me than Ali.” May Allah be pleased with all the Companions.
This hadith highlights Ali bin Abi Talib’s virtue and prohibits disliking him. End.
Saheehus-Seerah 