In the Holy Qur'an

Woe to those who pray but who are unmindful of their prayers (107:4-5)

Establish the prayer for My remembrance (20:14)

DO not be amongst those who are unmindful (7:205)

In the Traditions

The Prophet said, "Know that Allah does not answer supplication from a heedless and distracted heart."

The Prophet said, "Seize the opportunity to supplicate during tenderness (of heart) for verly it is a mercy."

The Propher said, "Whoever prays two cycles of prayer, and does not allow his mind to wander to the affairs of this world, will be forgiven for the wrong action he has committed earlier."

Imam Ali said, "Cajole your soul tactfully to worship, and be gently with it and do not force it. Make allowances for both its weariness and its activity, except for the daily obligations that are incumbent upon it, for it must fulfil them and undertake them at their prescribed times."