Do not be sad - Always remember Allah

Concerning His remembrance, Allah, the All-Glorious, says:

Verily, in the remembrance of Allah do hearts find rest. (Qur'an 13: 28)

Therefore remember me [by praying, glorifying etc.] and I will remember you…
(Qur'an 2: 152)

And the men and the women who remember Allah much with their hearts and tongues, Allah has prepared for them. Forgiveness and a Great reward [i.e. Paradise]. (Qur'an 33: 35)

You who believe! Remember Allah with much remembrance. And glorify His Praises morning and afternoon [the early morning (fajr) and ASR prayers. (Qur 'an 33: 41-42)

You who believe! Let not your properties or your children divert you from the remembrance of Allah. (Qur 'an 63: 9)

Aild remember your Lord when you fbrget... (Qur'an 18: 24)

And glory’s' the Praises of your Lord when you get up from sleep. And in the night-time also, glorify His Praises, -and at the setting of the stars. (Qur 'an 52: 48-49)

You who believe! When you meet [an enemy] force, take a firm stand against them and remember the Name of Allah much [both with tongue and mind], so that you may be successful. (Qur'an 8: 45)

In an authentic hadith, the Prophet (bpuh) said:

"The example of one who remembers his Lord in relation to one who does not remember his Lord is that of the living and the dead."

The Prophet (Blessings and Peace be upon him) also said:

"The mufarridoon outstrip others." His Companions asked. "Who are the mufarridoon, O' Messenger of Allah." He said, "The men who remember Allah often and the women who remember Allah often."

And in another authentic hadith, the Prophet (bpuh) said:

"Shall I not inform you of the best of deeds, and the purest of them with your Lord? The deed which is better for you than spending gold and silver (for a good cause). And which is better for you than to meet your enemy. And you cut their throats and they cut yours?" They said, "Yes_ O' Messenger of Allah." He said, "The remembrance of Allah."

The following is an authentic hadith:

"A man came to the Prophet and said, Messenger of Allah, the commandments of Islam have become too much for me, and I am old in age; so inform of something that I can adhere to.' He said, `That your tongue (continually) remains moist with the remembrance of Allah."

Source: Don't Be Sad - By Aaidh ibn Abdullah al-Qarni