When anyone of you prays towards an object that acts as a barrier between him and the people and then someone tries to pass in front of him, he should push him away; and if he insists, he should fight him, for indeed he is a devil
Authentic hadithعن أبي سعيد الْخُدْرِيِّ رضي الله عنه مرفوعًا: (إذا صلَّى أحدكم إلى شيء يَسْتُرُهُ من الناس، فأراد أحد أن يَجْتَازَ بين يديه فَلْيَدْفَعْهُ، فإن أبى فَلْيُقَاتِلْهُ؛ فإنما هو شيطان).
Abu Sa‘īd al-Khudri (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "When anyone of you prays towards an object that acts as a barrier between him and the people and then someone tries to pass in front of him, he should push him away; and if he insists, he should fight him, for indeed he is a devil."
Explanation
The Shariah enjoins caution and firmness in all matters. Prayer is the most important among all worldly and religious affairs. Therefore, the wise Lawgiver urges people to take care of it and orders the praying person to use something as a barrier between himself and the people so that they would not render his prayer deficient by passing in front of him as he worships his Lord and communicates privately with Him. If someone tries to pass before him, he should repel him in the easiest way possible. If he does not stop, however, he is no longer deemed inviolable, for he is now a transgressor. In such a situation, the only way to avert his aggression is to fight him by pushing him away forcefully. This is because his action is typical of the devils who seek to spoil people's acts of worship and cause them confusion during prayer.
Source · Narrated by Bukhari & Muslim
From the Hadith Encyclopedia (hadeethenc.com).