Should a Muslim defend a Christian colleague who is being persecuted and mistreated by Muslim co-workers demanding that he convert to Islam or leave, taking into account the noble Prophetic saying: "Support your brother whether he is an oppressor or oppressed"?

The described situation involves a grave error. While it is obligatory to detest a Christian for his disbelief, he must be treated with justice, fairness, and kindness as long as he is peaceful, and invited to Islam with goodly exhortation, as Allah Almighty says: "Allah does not forbid you from those who do not fight you because of religion and do not expel you from your homes - from being righteous toward them and acting justly toward them. Indeed, Allah loves those who act justly." (Quran 60:8). It is obligatory to address all people—Muslims and non-Muslims, except for those at war—with goodly speech, "and speak to people good words" (Quran 2:83). Insulting them is forbidden. As for the questioner's reliance on the hadith (definition) "Help your brother, whether he is an oppressor or oppressed," it is incorrect, for this hadith is specific to Muslims. However, aiding the oppressed is a religious obligation, even if the oppressed person is a non-Muslim, and what the Christian is subjected to is an injustice to him and to Islam. The questioner and his colleagues must adhere to the Islamic legal guidelines in dealing with the Christian and cooperate in inviting him with wisdom and goodly exhortation.