“Whoever is stricken with sadness, grief, sickness or hardship and says: ‘Allah is my Lord, without any partners’ [Allaahu Rabbi, laa shareeka lah], then it will be removed from him.” [‘Sahih al-Jami’ #6040]
Here is an excerpt from Ibnul Qayyim (rahimahullaah):
Indeed, there is an hour (opportune time) on Friday and if a Muslim gets it while praying and asks something from Allah, then Allah will definitely meet his demand. And he (salallaahu ‘alayhi wa sallam) pointed out the shortness of that time with his hands.
Aboo Dawood (rahimahullaah) reported (no. 345) from Aws ibn Aws ath-Thaqafee (radiallaahu ‘anhu): I heard Allaah’s Messenger (salallaahu ‘alaihi wa sallam) say:
“Whoever washes his head on the day of Jumu’ah, and takes a bath and arrives in time, and he walks and he does not ride, and he draws close to the imaam, and he listens and he does not speak. Then for every step which he takes, there will be for him the reward of a year: the reward of fasting it and standing in Prayer.”
Shaikh al-Albaanee (rahimahullaah) said this hadeeth is (saheeh) authentic.
Further Reading :
‘Arafah on Saturday 5ht November 2011 (9 Dhul-Hijjah 1432)
The ninth day of Dhul-Hijjah is the day of ’Arafah, since it is on this day that the pilgrims gather at the mountain plain of ’Arafah, praying and supplicating to their Lord.
It is mustahabb (highly recommended) for those who are not pilgrims to fast on this day, since the Prophet (sallallaahu ’alayhi wa sallam) was asked about fasting on the day of ’Arafah, so he said, “It expiates the sins of the past year and the coming year.” 
Likewise, the Prophet (sallallaahu ’alayhi wa sallam) said, ‘There is no day on which Allaah frees people from the Fire more so than on the day of ’Arafah. He comes close to those (people standing on ’Arafah), and then He reveals before His Angels saying, ‘What are these people seeking.” 
Imaam at-Tirmidhee (d.275H) – rahimahullaah – said, “The People of Knowledge consider it recommended to fast on the day of ’Arafah, except for those at ’Arafah.” 
 Related by Muslim (no. 1162), from Aboo Qataadah (radiyallaahu ’anhu).
 Related by Muslim (no. 1348), from ’Aa‘ishah (radiyallaahu ’anhaa).
 Refer to Jaami’ut-Tirmidhee (3/377).
- Excellence of Fasting on the Day of Arafah – from Al-Istiqaamah Magazine, Issue No.6
- Fasting on Day of Arafah for Different Moon Sighting Countries
- The best supplication offered on the Day of ‘arafaat is that of the Prophet Muhammad (peace be upon him)
- Al-Hajj Al-Akbar : What is the meaning of the “Day of the Greatest Hajj” and the “Greatest Hajj”?