The Key to the Saintly Path by Ibn Shaykh al-Hazzamiyyin is a primer into the science of tazkiya and sulūk. 

In it, he details practical steps that you can apply in your day-to-day endeavors that will help strengthen your spiritual connection with Allāh Almighty. If you are sincere and dedicated, He will eventually make you of His righteous servants.

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The videos below provide a similarly succinct explanation for proper understanding and application.