Many contemporary debates about Sufism, asceticism (zuhd), and legalism are settled by reading SifatuSafwa. Ibn al-Jawzi celebrates spiritual exertion without endorsing innovation (bid’ah). He shows that the early Muslims were both deeply legalistic in their adherence to the Qur’an and Sunnah and profoundly spiritual in their devotion.
Since I cannot provide direct download links, here are the best ways to obtain a digital copy: sifatusafwa ibn al-jawzi pdf