in front of the rest of the congregation. The mihrab became a part of the mosque during the Umayyad period and its form was standardised during the Abbasid period; before that, the qibla of a mosque was known from the orientation of one of its walls, called the qibla wall. The term mihrab itself is attested only once in the Quran, but it refers to a place of prayer of the Israelites rather than a part of a mosque. The Mosque of Amr ibn al-As in Fustat, Egypt, one of the oldest mosques, is known to have been built originally without a mihrab, though one has since been added. Ayn al-ka'bah and jihat al-ka'bah Ayn al-ka'bah ("standing so as to face the Kaaba head-on") is a position facing the qibla so that an imaginary line extending from the person's line of sight would pass through the Kaaba. This manner of observing the qibla is easily done inside the Great Mosque of Mecca and its surroundings, but given that the Kaaba is less than wide, this is virtually impossible from distant locations. For example, from Medina, with a straight-line distance from the Kaaba, a one-degree deviation from the precise imaginary line—an error hardly noticeable when setting one's prayer mat or assuming one's posture—results in a shift from the site of the Kaaba. This effect is amplified when further than Mecca: from Jakarta, Indonesia—some away, a one-degree deviation causes more than a shift, and even an arc second's deviation——causes a more than shift from the location of the Kaaba. In comparison, the construction process of a mosque can easily introduce an error of up to five degrees from the calculated qibla, and the installation of prayer rugs inside the mosque as indicators for worshipers can add another deviation of five degrees from the mosque's orientation. A minority of Islamic religious scholars—for example Ibn Arabi (d. 1240)—consider ayn al-ka'bah to be obligatory during the ritual prayer, while others consider it obligatory only when one is able. For locations further than Mecca, scholars such as Abu Hanifa (d. 699) and Al-Qurtubi (d. 1214) argue that it is permissible to assume jihat al-ka'bah, facing only the general direction of the Kaaba. Others argue that the ritual condition of facing the qibla is already fulfilled when the imaginary line to the Kaaba is within one's field of vision. For instance, there are legal opinions that accept