Fatima bt. Asad
No doubt that Lady Fatima Bint Asad was a great lady with high degree of Iman and dedication to Allah (SWT) and she was always supplicating to Allah (SWT). DU'A from her to Allah has great importance because of her sincerity which is very rare among people. Her DU'A is effective because of her great state of Iman and we can not expect same effect with Du'a from others.