Al-Arba'in al-Nawawiyyah (The Forty Hadith of al-Nawawi).
On the authority of Abu Hurayrah (may Allah be pleased with him), who said:
The Messenger of Allah (peace and blessings of Allah be upon him) said:
"Allah Almighty says:
'Whoever shows enmity to a devoted servant of Mine, I have declared war upon him.
And My servant does not draw near to Me with anything more beloved to Me than that which I have made obligatory upon him;
and My servant continues to draw near to Me with voluntary good deeds until I love him.
So when I love him, I become his hearing with which he hears, his sight with which he sees,
his hand with which he grasps, and his foot with which he walks. If he asks of Me, I will surely give him; and if he seeks refuge in Me, I will surely grant him refuge.'"
Related by al-Bukhari.
This hadith demonstrates the exalted station of the allies and devoted servants of Allah,
and that harming them or showing them enmity is among the most grave of sins,
because they are the people of obedience and closeness to Allah.
It also clarifies that the most beloved thing through which a servant draws near to Allah
is the performance of obligatory duties,
followed by performing abundant voluntary righteous deeds,
until he attains the love and divine guidance of Allah.
Thus, the hadith cultivates reverence for the righteous,
diligence in performing acts of worship,
and striving to attain Allah's love,
through which one achieves true success in both this world and the Hereafter.