Hadith #1

عَنْ أَمِيرِ الْمُؤْمِنِينَ أَبِي حَفْصٍ عُمَرَ بْنِ الْخَطَّابِ رَضِيَ اللهُ عَنْهُ قَالَ: سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ: " إنَّمَا الْأَعْمَالُ بِالنِّيَّاتِ، وَإِنَّمَا لِكُلِّ امْرِئٍ مَا نَوَى، فَمَنْ كَانَتْ هِجْرَتُهُ إلَى اللَّهِ وَرَسُولِهِ فَهِجْرَتُهُ إلَى اللَّهِ وَرَسُولِهِ، وَمَنْ كَانَتْ هِجْرَتُهُ لِدُنْيَا يُصِيبُهَا أَوْ امْرَأَةٍ يَنْكِحُهَا فَهِجْرَتُهُ إلَى مَا هَاجَرَ إلَيْهِ". رَوَاهُ إِمَامَا الْمُحَدِّثِينَ أَبُو عَبْدِ اللهِ مُحَمَّدُ بنُ إِسْمَاعِيل بن إِبْرَاهِيم بن الْمُغِيرَة بن بَرْدِزبَه الْبُخَارِيُّ الْجُعْفِيُّ [رقم:1]، وَأَبُو الْحُسَيْنِ مُسْلِمٌ بنُ الْحَجَّاج بن مُسْلِم الْقُشَيْرِيُّ النَّيْسَابُورِيُّ [رقم:1907] رَضِيَ اللهُ عَنْهُمَا فِي "صَحِيحَيْهِمَا" اللذَينِ هُمَا أَصَحُّ الْكُتُبِ الْمُصَنَّفَةِ. 

It is narrated on the authority of Amirul Mu'minin, Abu Hafs 'Umar bin al-Khattab (ra) who said:

I heard the Messenger of Allah (ﷺ) say: "Actions are (judged) by motives (niyyah), so each man will have what he intended. Thus, he whose migration (hijrah) was to Allah and His Messenger, his migration is to Allah and His Messenger; but he whose migration was for some worldly thing he might gain, or for a wife he might marry, his migration is to that for which he migrated." [Bukhari & Muslim]

https://sunnah.com/nawawi40:1

Explanation:

This Hadeeth is a great foundation regarding the actions of the heart due to the intentions stemming from the actions of the heart. The scholars have said: This Hadeeth is half of worship because it is the scale of the inward actions. As well, the Hadeeth of 'Aa'ishah, 

‏ مَنْ أَحْدَثَ فِي أَمْرِنَا هَذَا مَا لَيْسَ فِيهِ فَهُوَ رَدٌّ

"Whoever innovates into this affair of ours that which is not from it shall have it rejected." 

Al-Bukhaaree #2697 

https://sunnah.com/bukhari:2697 

And in another wording, 

‏من عمل عملاً ليس عليه أمرنا فهو رد

"Whoever does an action that is not from this affair of ours shall have it rejected.” 

Saheeh Muslim after Hadith #1718

https://sunnah.com/riyadussalihin:1647 

This Hadeeth is half of the Religion because it is the scale of the outward actions. So the benefit derived from his statement, 

"The reward of actions depends on their intentions." 

Meaning: there is no action except that it has an intention. That is because it is impossible for any person that has intellect and the ability of choice to perform an action without an intention. Even some of the scholars have said, "If Allaah were to burden us with actions without intentions, then there would be from responsibility that which no one could bear".