The directive to "beat them" is not an allowance at all, but a straightforward, matter-of-fact command. And the words وَاضْرِبُوهُنَّ, wa dariboohunna, do not just mean "and chastise them." They mean "and beat them," and that or a variant of that is how they are uniformly translated:
Pickthall: “and scourge them”
Yusuf Ali: “(And last) beat them (lightly)”
Al-Hilali/Khan: “(and last) beat them (lightly, if it is useful)”
Shakir: “and beat them”
Sher Ali: “and chastise them”
Khalifa: “then you may (as a last alternative) beat them”
Arberry: “and beat them”
Dawood: "and beat them"
Rodwell: “and scourge them”
Sale: “and chastise them”
Asad: “then beat them”
Daryabadi: "and beat them"
Aisha reports that Muhammad struck her. Once he went out at night after he thought she was asleep, and she followed him surreptitiously. Muhammad saw her, and, as Aisha recounts: “He struck me on the chest which caused me pain, and then said: Did you think that Allah and His Apostle would deal unjustly with you?” (Sahih Muslim 2127) Aisha herself said it: “I have not seen any woman suffering as much as the believing women.” (Sahih Bukhari 7.72.715)
Laleh Bakhtiar, in a recent translation that has received wide publicity, translates it as “go away from them.” In light of this unanimity among the translators, both Muslim and non-Muslim, this seems difficult to sustain – all of these authorities got the passage wrong until Bakhtiar? But her impulse is understandable, as many Muslims today regard this verse with acute embarrassment. Muhammad Asad adduces numerous traditions in which Muhammad “forbade the beating of any woman,” concluding that wife-beating is “barely permissible, and should preferably be avoided.”
Unfortunately, however, this is not a unanimous view. The Koran commentary Ruhul Ma’ani reflects mainstream Muslim understandings of this verse when it gives four reasons that a man may beat his wife: “if she refuses to beautify herself for him,” if she refuses sex when he asks for it, if she refuses to pray or perform ritual ablutions, and “if she goes out of the house without a valid excuse.”
Also, Muhammad’s example is normative for Muslims, since he is an “excellent example of conduct” (Koran 33:21) – and according to a canonical hadith, Muhammad’s favorite wife, his child bride Aisha, reports that Muhammad struck her. Once he went out at night after he thought she was asleep, and she followed him surreptitiously. Muhammad saw her, and, as Aisha recounts: “He struck me on the chest which caused me pain, and then said: Did you think that Allah and His Apostle would deal unjustly with you?” (Sahih Muslim 2127) Aisha herself said it: “I have not seen any woman suffering as much as the believing women.” (Sahih Bukhari 7.72.715)