• To place a Sutrah for prayer is Sunnah in our Maddhab regardless if you fear that someone will cross in front of you or not. This applies to both the Imam and the one praying on their own, with the exception of the one praying with the Imam (regardless if they are standing behind the Imam or next to him).
• As for the Sutrah itself then the preferred height is approximately 1 cubit. There is no set preference for its thickness. If one had to choose between a tall Sutrah and a broad one, then Imam Ahmad (r) preferred broader ones over the taller.
So, the Sutrah can be anything thick like a wall or a pillar or something they can vertically erect in front of them. If erecting it is not possible then its fine for them to just lay it on the ground. If one is in an open land for example and cannot find anything at all then it suffices for them to just draw a line on the ground and take it as a Sutrah.
• If someone has placed a Sutrah in front of them for Salah, then whilst they are praying you are not allowed to pass in front of them, even if they have taken an unnecessarily large gap between them and the Sutrah.
If someone has not placed a Sutrah, then you can cross in front of them whilst maintaining a distance of 3 cubits starting from their feet. This measurement is taken from the report narrated by Imam Ahmad (r) and Bukhari (r) that the Messenger of Allah ﷺ prayed inside the Ka’bah with approximately 3 cubits between him and the wall.
The 3 cubit measurement is the official position and the opinion of most scholars within the Maddhab.
Al-Majd (r) said, “This is the stronger position in my view.”
This was also confirmed as the official position by Ibn Muflih (r), Ibn Hamdan (r), ‘Ali b. Muhammad al-Ba’li (r), and Ibn Qadi al-Jabal (r).
• There are 3 occasions in which you may allow yourself to be crossed in Salah:
1) If you you tried to stop the person/thing crossing but you were overcome.
2) If the person/thing had a need to cross. The “need” here was explained by Ibn Qaid (r) to mean the need to cross due to the narrowness of the path.
3) If you were in Makkah. So if you are praying in Makkah and someone was passing in front of you well within 3 cubits, then in this case you don’t attempt to stop them but just allow them to pass.
• If one needs to cross, then he may take something and place it in front of the one praying and then cross. This was stated by al-Samurri (r).
• It is important to note that standing in front of the one praying is not the same as crossing in front of them. The impermissibility does not apply to going and standing in front of the one praying, but it applies to crossing fully. So if, for instance, one needed to take something and it was in front of the Musalli then they can go in front of them and take that thing as long as they didn’t fully cross. This was stated by al-Buhuti (r).
[Refer to: al-Rawd; Sharh al-Muntaha; al-Kasshaf; al-Insaf]