The Success is for the believers who with their Salah are Khashi`un.

The Success is for the believers who with their Salah are Khashi`un. 
ﺃﻋﻮﺫ ﺑﺎﻟﻠﻪ ﻣﻦ ﺍﻟﺸﻴﻄﺎﻥ ﺍﻟﺮﺟﻴﻢ 
بِسْمِ اللَّهِ الرَّحْمَٰنِ الرَّحِيمِ
قَدْ أَفْلَحَ الْمُؤْمِنُونَ 
Translation and commentary from Ibn Kathir
(Successful indeed are the believers) means, they have attained victory and are blessed, for they have succeeded. These are the believers who have the following characteristics:
﴿الَّذِينَ هُمْ فِى صَلاَتِهِمْ خَـشِعُونَ ﴾
(Those who with their Salah are Khashi`un.) `Ali bin Abi Talhah reported that Ibn `Abbas said:
﴿خَـشِعُونَ﴾
"(Khashi`un) means those with fear and with tranquillity.'' This was also narrated from Mujahid, Al-Hasan, Qatadah and Az-Zuhri. It was reported from `Ali bin Abi Talib, may Allah be pleased with him, that Khushu` means the Khushu` of the heart. This was also the view of Ibrahim An-Nakha`i. Al-Hasan Al-Basri said, "Their Khushu` was in their hearts.'' So they lowered their gaze and were humble towards others. Khushu` in prayer is only attained by the one who has emptied his heart totally, who does not pay attention to anything else besides it, and who prefers it above all else. At that point it becomes a delight and a joy for eyes, as in the Hadith recorded by Imam Ahmad and An-Nasa'i from Anas, who said that the Messenger of Allah said:
«حُبِّبَ إِلَيَّ الطِّيبُ وَالنِّسَاءُ، وَجُعِلَتْ قُرَّةُ عَيْنِي فِي الصَّلَاة»
(Fragrance and women have been made dear to me, and Salah was made the joy of my eye.)