Ibrahim ibn Adhaam, a 3rd century (Hijri) scholar, was asked concerning the verse,
"And your Lord says, 'Call on Me, I will answer your prayer...' " (40:60).
The people said to him, "We supplicate and we are not answered."
He responded to their concern, informing them why the supplications (du'a) were not answered,
"You know Allah, yet you do not obey Him.
You recite the Qur'an, yet you do not act according to it.
You know Shaitan, yet you have agreed with him.
You proclaim you love the Messenger of Allah (saw), yet you abandon his sunnah.
You proclaim your love for Paradise, yet you do not act to gain it.
You proclaim your fear for the Fire, yet you do not prevent yourselves from sins.
You say, 'Indeed death is true', yet you have not prepared for it.
You busy yourselves with finding faults with others, yet you do not look at your own faults.
You eat that which Allah has provided for you, yet you do not thank Him.
You bury your dead, yet you do not take a lesson from it."
(Ibn Rajab, Khusoo fis-Salat, p.62)