لا تصل الاّ الى السترة
Do not pray except in the direction (or towards) a sutrah (a screen or cover)… Ibn Khuzayma (1/93/1).
The Sutrah in the ordinary linguistics usage refers to a cover or a screen; which hides someone or something. In the Islamic terminology, Sutrah refers to that which one places before oneself while praying. It serves as a shield in which no one can pass between the one praying and the Sutrah.
There is a myriad of narration from the Prophet ﷺ – mentioning the importance of Sutrah. This Hadith, for instance, is a direct directive from Allah’s messenger ﷺ. In another Hadith reported in the Sahihayn (Bukhari and Muslim), from Aboo Hurayrah, the Prophet ﷺ mentioned that it is better for a person to wait for forty (days, months or years) rather than pass between the one praying and the Sutrah.
The Imam of the scholars of hadeeth in this era, Al-Imam Nasirudeen al-Albani in his treatise of immeasurable benefit, Description of the Prophet’s Prayer, he referenced from the above-quoted hadith that the Sutrah is obligatory. It is mandatory on the one who prays alone and the Imam, in case of a congregation.
The eminent shaykh, while dedicating a chapter on this, explained that the Sutrah is obligatory in both large and small Masaajid (mosques). He decried the dearth of this practise and therefore charged Imams of Masaajid and People of Knowledge to educate the people on the essentiality of the Sutrah.
In addendum, the Sutrah can equally be a person, animal or any other thing, as indicated in hadiths of the Prophetﷺ, particularly the hadith of ‘Aisha where she described that the Prophet ﷺ prayed while using her leg as the Sutrah. The length of the Sutrah is that of a forearm, approximately two-thirds of a cubit. The Sutrah can be as thick as the wall or as thin as the arrow. The height can relatively be the height of the back of a saddle but anything that comes short of this can equally be used.
Lastly, the one praying is to stay close to the Sutrah and not allow anyone to pass between them. The distance should be so close, barely spacious for a sheep to pass.
Although, some scholars hold a divergent opinion on the obligation of the sutrah and rather hold that it is only recommended. The availability of evidence and scholastic interpretations in support of the former opinion, however, seems most weighty and most convincing.
And Allah knows Best.