Sahih al-Bukhari and Sahih Muslim report that Aisha was six when her marriage contract with the Prophet Muhammad (peace and blessings be upon him) was made and nine when she joined his household. Critics say this shows the Prophet acted immorally and that Islam permits child marriage.
“Narrated `Aisha: that the Prophet married her when she was six years old and he consummated his marriage when she was nine years old, and then she remained with him for nine years (i.e., till his death).”Sahih al-Bukhari 5133, grading: Sahih (in Sahih al-Bukhari). English translation as given on sunnah.com
Most Muslim scholars accept these reports as authentic. Ibn Hazm, Ibn Kathir and Ibn Abd al-Barr each recorded that there was no disagreement over her age, as a Yaqeen Institute paper documents. A minority of modern scholars, notably the Syrian hadith scholar Salah al-Din al-Idlibi (presented by Arnold Yasin Mol at Yaqeen Institute), argue from other reports and the biographical sources that she was about fourteen at the contract and nearly eighteen when the marriage began, and that the age in this narration is a narrator's error. This page answers the charge on the basis of the majority position, since it is the strongest form of the objection.
Marriage around puberty was the norm across the premodern world, not a feature of Arabia alone. Roman law set the age of marriage for girls at twelve. The Catholic Church adopted that rule into canon law, and the twelfth-century canonist Gratian held that a girl could consent to marriage at twelve. The Church raised the minimum for girls to fourteen only in 1917. English law also used twelve, and this became the default minimum in colonial America until individual states raised it.
The Prophet's opponents in Mecca and Medina accused him of being a madman, a sorcerer and a poet, and they looked for anything to use against him. No report records any of them objecting to this marriage. Yaqeen Institute's researchers make this point: the controversy is modern, and it rests on judging a seventh-century marriage by twenty-first-century norms.
And test the orphans [in their abilities] until they reach marriageable age. Then if you perceive in them sound judgement, release their property to them. And do not consume it excessively and quickly, [anticipating] that they will grow up. And whoever, [when acting as guardian], is self-sufficient should refrain [from taking a fee]; and whoever is poor - let him take according to what is acceptable. Then when you release their property to them, bring witnesses upon them. And sufficient is Allah as Accountant.Quran 4:6, Sahih International
The Quran links "marriageable age" to maturity and sound judgement rather than to a fixed number of years (Quran 4:6), and Islamic law conditions the start of married life on physical and mental readiness. Because the age is tied to welfare and readiness, Muslim jurists accept that a government may set a minimum age suited to its time, and many Muslim-majority countries do so today.
Aisha spoke of her marriage with affection, became one of the leading scholars of the first generation, and is credited with narrating more than 2,210 hadith. Companions and later scholars came to her for rulings on law and the Prophet's practice. Her own life does not fit the picture the criticism draws.
Most Christian and Jewish critics apply a different standard to their own tradition.
Now therefore kill every male among the little ones, and kill every woman who has known man by lying with him. But all the girls, who have not known man by lying with him, keep alive for yourselves.Numbers 31:17-18, World English Bible (public domain)
This passage concerns captives taken in war, not a marriage contract, and commentators differ on what "for yourselves" means. It shows that the Bible sets no minimum age, and that young girls were taken "for yourselves" with no age limit at all.
The clearer comparison is the Church's own law. For most of Christian history canon law allowed a girl to marry at twelve, and the Catholic Church raised this only to fourteen, in 1917. Christians do not conclude that every bishop and priest who blessed such marriages over nineteen centuries was immoral; they judge them by their time. The same fairness is owed to a marriage contracted in seventh-century Arabia, where the norm was the same and no contemporary objected.
Quran quotations: Sahih International via quran.com. Hadith quotations: the English translations and gradings shown on sunnah.com. Bible quotations: World English Bible (public domain).