mgawdno:

Imam al-Shafi’i remarked, “There is a verse in the Quran that every wrongdoer should be terrified of.”

He was asked, “Which verse is that?” 

He replied, “‘And your Lord never forgets.’” [Surah Maryam: 64]

The servant speaks words that he does not understand its repercussions but he sinks down in Hell-Fire farther than the distance between the east and the west.
Muslim

The Prophet (peace be upon him) said: A Muslim has six rights over another Muslim.

They asked: “What are they, O Messenger of Allah?”

He said:
When you meet him, greet him with peace.
When he invites you, accept his invitation.
When he seeks your advice, advise him.
When he sneezes and then praises Allah, invoke Allah’s blessings upon him.
When he falls ill, visit him.
When he dies, follow his funeral.

[Sahîh Muslim]
When the month of Ramadan starts, the gates of the heaven are opened and the gates of Hell are closed and the devils are chained.
Bukhari
Narrated Anas: Allah’s Apostle (peace be upon him) said, “Help your brother, whether he is an oppressor or he is an oppressed one.” People asked, “O Allah’s Apostle! It is all right to help him if he is oppressed, but how should we help him if he is an oppressor?” The Prophet said, “By preventing him from oppressing others.”
Bukhari
The real patience is at the first stroke of calamity.
Bukhari 
One of the wives of Umar (bin Al-Khattab) used to offer the Fajr and the ‘Isha’ prayer in congregation in the Mosque. She was asked why she had come out for the prayer as she knew that Umar disliked it, and he has great ghaira (self-respect). She replied, “What prevents him from stopping me from this act?” The other replied, “The statement of Allah’s Apostle (peace be upon him) : ‘Do not stop Allah’s women-slave from going to Allah s Mosques’ prevents him.”
Bukhari
Oh Allah, there is no ease other than what You make easy. If You please, You ease sorrow.
Invocation for when you find something becoming difficult for you - Fortress of the Muslim