You have a lot transfers to make.
First, take bus 547 from Beixiaohexi (229m or so from Lize East Street) to Chengtie Wangjingxizhan
And then take subway line 13 from Wangjingxizhan Station to Dongzhimen Station.
Transfer to subway line 2 at Dongzhimen Station and get off at Changchunjie Station.
Lastly, take bus 10 from Changchunjielukoubei to Niujie Mosque. haha, here it is.