Justification for that comes from the fact that the prophet Muhammad’s favorite wife, Aisha, was six-years-old when he married her and nine when he consummated the marriage.
100%FedUp (h/t Marin W) Forced child marriages in Islam are widespread and are most prevalent in Pakistan, Afghanistan, followed by other Muslim countries in the Middle East and South Asia. Despite the law against child brides in Afghanistan, more than half of all girls are married before they turn 15, some before puberty.
Pakistani family pleads to keep their 6-year-old child out of a forced marriage as a way to settle a family feud. Young girls are often used as bargaining chips to settle monetary issues with neighbors or business associates.