I say: as this ḥadith itself indicates.
– “Let him draw a line”: the verb is khaṭṭa–yakhuṭṭu–khaṭṭan, meaning to make a mark. The plural of khaṭṭ (line) is khuṭūṭ.
Al-Miṣbāḥ states: “He drew on the ground” means he set a mark, and that is what is intended here—drawing a line in front of the person praying so that it serves as his sutra.

Benefits derived from the ḥadith

1. It is recommended—and emphatically so—to place a sutra in front of the worshipper, because of the many commands concerning it.
2. The sutra may be anything that protrudes directly before the worshipper’s face, preventing people from walking across his qiblah or the place of his prostration.
3. If he cannot find something prominent, it should be the height of the rear end of a rider’s saddle, above the camel’s hump; if he cannot obtain that, he moves to what is below it.
4. If he finds nothing at all, he should set up a staff. Al-Bukhārī (473) and Muslim (503) relate from Abū Juḥayfah that “the Prophet ﷺ prayed for them on the open plain, and in front of him there was an ʿanaza.” The ʿanaza is a stick with a fine iron tip. It is permissible to plant the stick in the ground, but better to place it crosswise so that it encloses the worshipper’s space and screens his entire qiblah side.
5. If he cannot find a staff, he should draw a line, placing it crosswise; it is preferable that it be curved like a miḥrāb. Abū Dāwūd said: “I heard Aḥmad say about the line: it should be like a crescent.”
6. When the worshipper sets up a sutra of any of these kinds, nothing that passes in front of him beyond it harms, diminishes, or invalidates his prayer.
7. By implication, if he does not place a sutra, his prayer is diminished—or invalidated—when someone passes close before him.
8. The plain purport of the ḥadith is that one should not resort to an inferior sutra until he fails to find a superior one, and that it