Two meanings of ṣarūrah should be recognized:
1. Tabattul or monastic withdrawal: leaving marriage and ordinary social duties under a notion of religious seclusion.
2. Pilgrimage usage: a person who has not yet performed Hajj.
Each usage needs its proper context. The educational point here is that withdrawing from lawful human responsibilities is not automatically a sign of superior religious devotion.
فِي الْإِسْلَامِ means “in Islam.” The preposition فِي governs the genitive ending in الْإِسْلَامِ.