I say, and with God's success: It is not permissible to exercise ijtihad in the fundamental and definitive principles of creed that are agreed upon by the Ahl al-Sunnah. As for the branches of uncertain creeds, it is permissible for scholars to exercise ijtihad in them, such as: the location of the basin, what al-Kawthar is, the shape of the Sirat, the ruling on the people of the period, and others. The reason for allowing ijtihad in these matters is either because the texts regarding them are uncertain, or because there is no text at all. And God knows best.