1. The Prophet (sallallahu alaiyhi wa sallam) said: “The slave who is stricken by grief or sorrow will not say the following prayer without it being answered and having his sorrow replaced by happiness:

“Oh, Allaah, I am your slave and the son of your slave and your female slave.  My progress is in Your Command, just is Your Judgement.  I ask You by each of Your Names, by which You have called Yourself or revealed in Your Book, or which You have taught to one of Your creatures, or which You have chosen to keep in Your Secret Knowledge to make the Qur’aan, the joy of my heart the light of my eyes, which removes my grief and drives away my sorrow, thus replacing it with happiness.” (Narrated by Imaam Ahmad and Ibn Hibbaan)

2.  The prayer of Yoonus in the belly of the whale:

(Soorah Al-Anbiyaa ‘21:87)

It is reported that the Prophet (sallallahu alaiyhi wa sallam) said: “If any Muslim supplicates with this prayer, it will be answered.” (Narrated by Imaam Ahmad and others)

3.  When the Prophet (sallallahu alaiyhi wa sallam) was sad, he used to pray:

“Oh, You the Ever-living, the Ever-lasting, by Your Mercy I seek help.”