Signs of the Sound Heart—Imaam Ibnul Qayyim (rahimahullaah)
Neither does it become lax in the remembrance of its Lord nor does it get tired of serving Him (i.e. carrying out acts of obedience and keeping away from disobedience). It does not become habituated with other than Him, except the one who directs it to its Lord; mentions Him to it and reminds it of this affair.
[Slightly paraphrased. Source: Ighaatha Al-Lahfaan page: 68]