Hazrat Mufti Ebrahim Salejee (Daamat Barakaatuhu) mentioned:
The hadeeth speaks of du‘aa being the essence of ‘ibaadat. In fact, one hadeeth states that du‘aa itself is ‘ibaadat. Apart from the various forms of ‘ibaadat that we do, we still need a way to secure the favours of Allah Ta‘ala. So this is through du‘aa.
Allah Ta‘ala teaches us the manner of du‘aa via the incident of Zakariyya (‘alaihis salaam). The first aspect is that it was “nidaa-an khafiyya” – he was not shouting out to Allah Ta‘ala and demanding from Him, rather it was silent with humility. The second aspect is that he expressed his weakness and inability – “My bones have become feeble and my hair has turned white.” We also need to show our weakness to Allah Ta‘ala, that we are always in need of Him. The third aspect is that we build our hope in Allah Ta‘ala – “I have never been turned down by You, O my Rabb.”
Du‘aas are always answered, they are never rejected. It is just that some du‘aas take time to materialise. It is like different seeds that you plant. Some may take one year to bear fruit and some may take ten to fifteen years. One should therefore go on begging from Allah Ta‘ala. And Allah Ta‘ala loves the tears of His servants. Therefore, at times there is a delay in the du‘aas being answered.
Source: Al-Haadi