Suuratul – Huud Verse 61.
وَإِلَىٰ ثَمُودَ أَخَاهُمْ صَـٰلِحًا ۚ قَالَ يَـٰقَوْمِ ٱعْبُدُوا۟ ٱللَّـهَ مَا لَكُم مِّنْ إِلَـٰهٍ غَيْرُهُۥ ۖ هُوَ أَنشَأَكُم مِّنَ ٱلْأَرْضِ وَٱسْتَعْمَرَكُمْ فِيهَا فَٱسْتَغْفِرُوهُ ثُمَّ تُوبُوٓا۟ إِلَيْهِ ۚ إِنَّ رَبِّى قَرِيبٌ مُّجِيبٌ ﴿٦١
61. And to Thamud (people, We sent) their brother Salih (Saleh). He said: “O my people! Worship Allah, you have no other Ilah (God) but Him. He brought you forth from the earth and settled you therein, then ask forgiveness of Him and turn to Him in repentance. Certainly, my Lord is Near (to all by His Knowledge), Responsive.”
Tafsir Ibn Kathir
He (Salih) commanded them to worship Allah alone. He said to them,
﴿إِنَّ رَبِّى قَرِيبٌ مُّجِيبٌ﴾
Certainly, my Lord is Near (to all by His knowledge), Responsive.
This is similar to Allah’s statement,
﴿وَإِذَا سَأَلَكَ عِبَادِي عَنِّي فَإِنِّي قَرِيبٌ أُجِيبُ دَعْوَةَ الدَّاعِ إِذَا دَعَانِ﴾
And when My servants ask you concerning Me, then (answer them), I am indeed Near (to them by My knowledge). I respond to the invocations of the supplicant when he calls on Me. (2:186)
Imam Ahmad reported that Abu Musa Al-Ash`ari said, “We were in the company of Allah’s Messenger during a battle. Whenever we climbed a high place, went up a hill or went down a valley, we used to say, `Allah is the Most Great,’ raising our voices. The Prophet came by us and said:
«يَا أَيُّهَا النَّاسُ، ارْبَعُوا عَلى أَنْفُسِكُمْ، فَإِنَّكُمْ لَا تَدْعُونَ أَصَمَّ ولَا غَائِبًا، إنَّمَا تَدْعُونَ سَمِيعًا بَصِيرًا، إنَّ الَّذي تَدْعُونَ أَقْربُ إِلَى أَحَدِكُمْ مِنْ عُنُقِ رَاحِلَتِهِ، يا عَبْدَاللهِ بْنَ قَيْسٍ، أَلَا أُعَلِّمُكَ كَلِمَةً مِنْ كُنُوزِ الْجَنَّةِ؟ لَا حَوْلَ وَلَا قُوَّةَ إِلَّا بِالله»
(O people! Be merciful to yourselves (i.e., don’t raise your voices), for you are not calling a deaf or an absent one, but One Who is All-Hearer, All-Seer. The One Whom you call is closer to one of you than the neck of his animal. O `Abdullah bin Qais (Abu Musa’s name) should I teach you a statement that is a treasure of Paradise: `La hawla wa la quwwata illa billah.
Furthermore, Imam Ahmad recorded that Anas said that the Prophet said:
«يَقُولُ اللهُ تَعَالى أَنَا عِنْدَ ظَنِّ عَبْدِي بِي وَأَنَا مَعَهُ إِذَا دَعَانِي»
“Allah the Exalted said, `I am as My servant thinks of Me, and I am with him whenever he invokes Me.’
Imam Ahmad also recorded Abu Sa`id saying that the Prophet said:
No Muslim supplicates to Allah with a Du`a that does not involve sin or cutting the relations of the womb, but Allah will grant him one of the three things. He will either hasten the response to his supplication, save it for him until the Hereafter, or would turn an equivalent amount of evil away from him.”
They said, “What if we were to recite more (Du`a).” He said, (There is more with Allah.)