What is the maximum number of wives allowed in Islam(polygyny/polygamy)?

The four main schools of Islamic law limit the maximum number of wives a man marry to four based on the following Qur'anic verse often supplemented by numerous ahadith especially the narration from Aḥmad who said that the Prophet (saw) ordered Ghaylan Salmah ibn al-Thaqaafi who converted to Islam to choose four of his ten wifes (ikhtar minhunna arba'ari). The key verse comprises: "If you fear you will not deal fairly with orphan girls, marry other women who seem good to you, two, three and four. If you fear you cannot be equitable [to them], then marry only one, or your slave(s): that is more likely to make you avoid bias..." (Qur'an 4:3) The historical context of the verse is explained when Urwa narrates that he asked Aisha about this verse and she said,: "O my nephew! (This verse was revealed in connection with) an orphan girl under the guardianship of her guardian who is attracted by her wealth and beauty and intends to marry her with a mahr less than what other women of her standard deserve. So they (such guardians) have been forbidden to marry them unless they do justice to them and give them their full mahr, and they are ordered to marry other women instead of them." (Sahih al-Bukhari) The Zahiri school of law however argued polygyny may be up to a maximum of nine wives. Their argument is based on the use of wau in the verse, which holds the original meaning to add numbers, therefore mathna, thulatha and ruba mean two plus three plus four equals nine. This is in accordance with the behavior of the Prophet (saw) who had nine wives. They even assume if a man had less than nine wives, then he is then considered to not follow the sunnah. (al-Jashshash, Ahkam al-Qur'an) The Mutazalite jurist and mufassir al-Zamakshari held a similar view regarding 9 being the maximum. (Tafsir al-Kasyaaf, Vol. I) The Khawarij argued polygynous marriages can be performed with 18 wives. They translate mathna as two-two to show repeatedly twice, thulatha is three-three equals six and ruba is four-four equals eight, the total number being eighteen.