Sayyiduna Waqid (may Allah be pleased with him), the freed slave of the Prophet (peace and blessings be upon him), narrates that the Prophet (peace and blessings be upon him) said: "Whoever obeys Allah Almighty has, as it were, remembered Him, even if his (voluntary) prayer, fasting or recitation of the Qur'an is little; and whoever disobeys Allah Almighty has not remembered Allah Almighty, even if his prayer, fasting and recitation of the Qur'an are abundant."
This narration was recorded by Imam al-Tabarani in al-Mu'jam al-Kabir; its chain contains a narrator, al-Haytham bin Jimaz, who is matruk (abandoned).