“It is reported from Aisha that she said: The Prophet entered into marriage with me when I was a girl of six … and at the time [of joining his household] I was a girl of nine years of age.
As to the authenticity of these reports, it may be noted that the compilers of the books of Hadith did not apply the same stringent tests when accepting reports relating to historical matters as they did before accepting reports relating to the practical teachings and laws of Islam. The reason is that the former type of report was regarded as merely of academic interest while the latter type of report had a direct bearing on the practical duties of a Muslim and on what was allowed to them and what was prohibited. Thus the occurrence of reports such as the above about the marriage of Aisha in books of Hadith, even in Bukhari, is not necessarily a proof of their credibility.
It appears that Maulana Muhammad Ali was the first Islamic scholar directly to challenge the notion that Aisha was aged six and nine, respectively, at the time of her nikah and consummation of marriage. This he did in, at least, the following writings: his English booklet Prophet of Islam, his larger English book Muhammad, the Prophet, and in the footnotes in his voluminous Urdu translation and commentary of Sahih Bukhari entitled Fadl-ul-Bari, these three writings being published in the 1920s and 1930s. In the booklet Prophet of Islam, which was later incorporated in 1948 as the first chapter of his book Living Thoughts of the Prophet Muhammad, The evidence are listed below with other researches
According to a hadith in Bukhari and Muslim, Aisha is said to have joined Muhammad on the raid that culminated in the Battle of Badr, in 624 CE. However, because no one below the age of fifteen was allowed to accompany raiding parties, Aisha should have been at least fifteen in 624 CE and thus at least thirteen when she was married following the Hijra in 622 CE.
Ibn Hisham’s version of Ibn Ishaq’s Sirat Rashul Allah, the earliest surviving biography of Muhammad, records Aisha as having converted to Islam before Umar ibn al-Khattab, during the first few years of Islam around 610 CE. In order to accept Islam she must have been walking and talking, hence at least three years of age, which would make her at least fifteen in 622 CE.
Tabari reports that Abu Bakr wished to spare Aisha the discomforts of a journey to Ethiopia soon after 615 CE, and tried to bring forward her marriage to Mut`am’s son. Mut`am refused because Abu Bakr had converted to Islam, but if Aisha was already of marriageable age in 615 CE, she must have been older than nine in 622 CE.
Tabari also reports that Abu Bakr’s four children were all born during the Jahiliyyah (Pre-Islam Period), which has ended in 610 CE, making Aisha at least twelve in 622 CE.
According to Ibn Hajar, Fatima was five years older than Aisha. Fatima is reported to have been born when Muhammad was thirty-five years old, meaning Aisha was born when he was forty years old, and thus twelve when Muhammad married at fifty-two.
According to the generally accepted tradition, Aisha was born about eight years before Hijrah (Migration to Medina). However, according to another narrative in Bukhari (Kitaab al-Tafseer) Aisha is reported to have said that at the time Surah Al-Qamar, the 54th chapter of the Qur’an , was revealed, “I was a young girl”. The 54th Surah of the Qur’an was revealed nine years before Hijrah. According to this tradition, Aisha had not only been born before the revelation of the referred Surah, but was actually a young girl, not even only an infant at that time. So if this age is assumed to be 7 to 14 years, then her age at the time of marriage would be 14 to 21.
According to almost all the historians, Asma the elder sister of Aisha, was ten years older than Aisha. It is reported in Taqreeb al-Tehzeeb as well as in Ibn Kathir’s Al-Bidayah wa al-Nihayah that Asma died in the 73rd year after migration of Muhammad when she was 100 years old. Now, obviously if Asma was 100 years old in the 73rd year after Migration to Medina, she should have been 27 or 28 years old at the time of migration. If Asma was 27 or 28 years old at the time of hijrah, Aisha should have been 17 or 18 years old at that time. Thus, if Aisha got married in year 1 AH or 2 AH (after Migration to Medina), she must have been between 18 to 20 years old at the time of her marriage.
According to many Ahadith in Bukhari, it is believed Aisha participated in the both of Badr and Uhud battles.
Furthermore, in Bukhari’s Kitabu’l-Maghazi, Ibn `Umar states: “The Prophet did not permit me to participate in Uhud battle, as at that time, I was 14 years old. But on the day of Khandaq battle, when I was 15 years old, the Prophet permitted my participation”. So, since it was not allowed for Muslims younger than 15 years old to participate in Uhud battle, Aisha, who participated in Uhud, must have been at least 15 years old in those battles; thus her age was at least 13 to 14 at the time of her marriage.
According to ibn Sa’d’s Tabaqat and Ansab al-Ashraf books, opinions are in disagreement concerning her marriage with Muhammad. The marriage seems to have taken place either two of five years after the Migration (Usd al-Ghaba, 5:501).
For further evidence, read: http://www.defence.pk/forums/current-events-social-issues/7816-hazrat-ayeshas-age-marriage.html
Even if she was in fact 9 years old, this marriage is still justified for the following reasons:
(a) She reached the age of puberty.
(b) The marriage happened 1400 ago, not today. At that time, their marriage was not considered unusual and the proof is that the enemies of Muslims at that time did not criticize this marriage. They attacked prophet Mohammad on many issues, yet they didn’t criticize his marriage to Aisha.
(c) The fact that prophet Mohammad married a 9-year old girl does not mean that we as Muslims can marry a 9-year girls today