biruni is obviously using the past tense that's all i can gather from the sentence so it can be any time before his time which would be pre turkic anyway but then again to answer your question we'd have to read the entire passage of the biruni quote to investigate the full chronological context it will take me a while after may the soonest before i can go to austin where they have a copy of the athar al baqiyah to shoot a picture of the page and post it on the talk page for all to view i'm currently stuck with commitments to attend to