The Prophet (SAW)
said: The best invocation is that of the Day of Arafat, and the best
that anyone can say is what I and the Prophets before me have said:
لا إِلَهَ إلاَّ اللهُ وَحْدَهُ لا شَريكَ لَهُ، لَهُ
المُلْكُ ولَهُ الحَمْدُ وهُوَ عَلَى كُلِّ شَيْءٍ قَديرٌ.
237. Laa 'ilaaha 'illallaahu wahdahu laa shareeka lahu, lahul-mulku wa
lahul-hamdu wa Huwa 'alaa kulli shay'in Qadeer.
None
has the right to be worshipped but Allah alone, Who has no partner. His
is the dominion and His is the praise, and He is Able to do all things.
Reference: At-Tirmithi.
Al-Albani graded it good in Sahih At-Tirmithi 3/184, and also
Silsilatul-'Ahadith As-Sahihah 4/6.
“Prayer (Salat) is the most important practice in Islam. Allah has ordered the Muslims to be mindful of it. The Holy Qur'an says:"Guard strictly your prayers, especially the Middle Prayer, and stand before Allah with all devotion.”