How to start fair treatment between two wives
Question

                If a man marries a second wife, how should he start fair treatment between his two wives?
Praise be to Allah. 
          Ibn Qudaamah said: If he marries a virgin, he should 
          stay with her for seven nights, then start alternating (between his 
          wives). If he marries a previously-married woman, then he should stay 
          with her for three nights. That is because Abu Qulaabah narrated that 
          Anas (may Allaah be pleased with him) said: “It is part of the Sunnah, 
          if a man marries a virgin after marrying a previously-married woman, 
          that he should stay with her for seven days, then start sharing his 
          time, and if he marries a previously-married woman, he should stay with 
          her for three days, then start sharing his time.” Abu Qulaabah said: 
          If you wish, you may say that Anas attributed this to the Prophet 
          
          (peace and blessings of Allaah be upon him) and it is agreed upon.  
          If the previously-married woman wants him to stay with her for seven 
          days, then he should do that, and make it up to the other wives later 
          on , because Umm Salamah narrated that the Messenger of Allaah 
          
          (peace and blessings of Allaah be upon him) stayed with her for three 
          days, and he said, “You are not unimportant; if you want I can stay 
          seven nights with you, but if I do that, I have to do likewise with 
          the rest of my wives.” According to another version, “If you wish, I 
          will stay with you for three nights, then I will alternate among you.” 
          According to another report: “If you wish, I will stay with you for 
          three nights exclusively for you.”