Reference: Majmoo’ Fataawa wa Rasaa.il Muhammad ibn Saalih al-‘Uthaymeen – Volume 13, Fatwa No.391
Question: [What is] the ruling of [performing] the prayer between the pillars?
Response: The [performance of the] prayer between the pillars is permissible when there is lack of space. As for when there is plenty [of space], then one should not pray between the pillars because that splits the [continuity of the] rows.