Question: What Persian general took advantage of Nasr ibn Sayyar being preoccupied with a civil war? 
Sentence (from "Nasr ibn Sayyar"): Naṣr ibn Sayyār al-Lāythi al-Kināni (Arabic: نصر بن سيار الليثي الكناني‎ ‎ ; 663–748) was an Arab general and the last Umayyad governor of Khurasan in 738–748.
Relevant evidence: No