How Might One Obtain Ikhlaas? – by Imâm Ibn Qayyim al-Jawziyyah
Ikhlaas cannot coexist in a heart which [embraces] the love of praise and commendation, [nor] the yearning [to obtain] that which is possessed amongst the people, save in the [manner] that fire and water, or a lizard and fish may coexist.
 How does one Attain Sincerity? – troid.ca
A brief excerpt from Imaam Ibnul-’Uthaymeen’s explanation of Riyaadus-Saaliheen demonstrating the importance of sacrifice as a means to attain piety and sincerity.
The Hadeeth of Intention – Imaam Ibn Rajab al-Hanbali
Ibn Rajab provides an excellent explanation of the niyyah from the well known hadeeth of ‘Umar ibn al-Khattaab. Many statements from the Salaf and additional hadeeth texts
The Acceptable Action – From Hussain Al-Awaa’ishahs Kitaab Ul-Ikhlaas – Abu Iyaad
Stressing the importance of correct intention and actions conforming to the Book and the Sunnah and how they are two conditions for the acceptable action