Salih always taught his disciples, "Who knocks at the door of someone constantly, one day the door must be opened to him."
Rabia one day heard it and said, "Salih, how long will you go on preaching thus, using the future tense, saying, 'will be opened?' Was the door ever closed?"
Salih bowed in submission to her.
- Fariduddin Attar
From Essential Sufism