Hazrat Shaikh Moulana Muhammad Zakariyya (rahmatullahi ‘alaih) writes:

The Soofiya have written that salaah in reality is an ‘ibaadat wherein one supplicates to Allah Ta’ala and communicates with Him. Therefore one needs to have concentration during salaah as the salaah cannot be discharged with negligence. In the case of other ‘ibaadaat, even though one does not possess a high level of concentration, the ‘ibaadat will take place. Consider the example of zakaat, the essence of zakaat is to spend money for the pleasure of Allah Ta’ala. Spending in itself is so hard on a person that even if he does it inattentively he would feel the pinch of it. Similarly, fasting requires giving up eating and drinking and sexual satisfaction. All these restrictions are extremely difficult on the soul. Even if they are not observed with proper attention and devotion, the ‘ibaadat will be discharged. On the other hand, zikr and recitation of the Quraan are the chief constituents of salaah. If these are not done attentively with devotion and concentration, they will not constitute supplication and communication with Allah Ta’ala. (Fazaail-e-A’amaal

[urdu], Fazaail-e-Namaaz pg. 87)

Source: Ihyaauddeen.co.za