The Meaning of Backup
Nusrah linguistically: nasarahu `ala `aduwwihi nasarahu nasran (he backed him up against his enemy such a backup); meaning he supported and strengthened him. The noun is nusrah - backup.  Abridged from: al-`Ayn, al-Khalil (2/35); Tahdhib al-Lughah, al-Azhari (4/197); Lisan al-`Arab, Ibn Manzur (5/210); al-Misbah al-Munir, al-Fayyumi (2/607); al-Qamus al-Muhit, al-Fayruzabadi (1/621); Taj al-`Arus, al-Zabidi (1/3538).
Nusrah technically: is protective and faithful jealousy, inciting one to uplift tyranny from one’s oppressed Muslim brother.  Hadhihi Akhlaquna, Mahmud al-Khazandar (p. 57). The Difference between Backup, Support (I`anah), and Aid (Ma`unah)
Backup is only against a persistent, hostile, incorrigible enemy. Support may be in that and in other than it. You may say: ‘He supported him against his oppressor and repelled him, and supported him during his poverty,’ if one aids another by giving him what would support him. You may also say: ‘He supported him in bearing what he needed to bear.’ One may not use ‘backup’ in those contexts though. In this breadth, it may be said that support is general, while backup is specific. Backup is through aid against the enemy. Aid is general in all such contexts. Every backup is a form of aid, but not vice versa.  al-Furuq al-Lughawiyyah, al-`Askari (p. 540). Encouragement towards Backup in the Qur’an and Sunnah
❖ Allah, exalted, says: “The believers are but brothers.” al-Hujurat: 10.
❖ He, exalted, also says: “Cooperate with one another in righteousness and piety, and do not cooperate in sin and aggression. Be mindful of Allah. Surely, Allah is severe in punishment.” al-Ma’idah: 2.
❖ He, exalted, says: “Those who believed, emigrated, and strived with their wealth and lives in the cause of Allah, as well as those who gave them shelter and help, they are truly guardians of one another. As for those who believed but did not emigrate, you have no obligations to them until they emigrate. But if they seek your help against persecution in faith, it is your obligation to help them, except against people bound with you in a treaty. Allah is All-Seeing of what you do.” al-Anfal: 72.
❖ The Prophet ﷺ said: “Back up your brother, be he the oppressor or the oppressed.” A man enquired: “Messenger of Allah, I back him up if he is oppressed. How do I do so if he is the oppressor?” He ﷺ replied: “You stop him - or prevent him - from oppression; this is how you back him up.”  Reported by al-Bukhari (6952) from the narration of Anas, Allah be pleased with him. Benefits of Backup
Allah purifying the Ummah from the evil of sin. Allah supports and gives victory to the state that backs up the oppressed, where he can take his right from the oppressor.  Majmu` al-Fatawa, Ibn Taymiyyah (28/146). Whoever backs up the oppressed, Allah backs him up. Reward is of the same nature as the deed. The Ummah’s salvation from punishment. If the Ummah does not take up the case of the oppressed, reprimanding the oppressor and preventing him from his oppression, then punishment will descend upon the whole Ummah. For he who aids others, Allah will facilitate for him those who will aid him in this life, and He will aid him in the next. Forms of Backup
Backing up: Before oppression takes place. By advising and rebuking the oppressor. By interceding for the oppressed. By alleviating the ruler’s oppression from him. In battle. Means to Acquiring the Quality of Backup
Recognising that supporting and backing up the oppressed is a form of obedience to Allah and His Messenger. In accordance with one’s love of Allah and His Messenger should be one’s obedience to them. Appreciating the brotherhood of faith. Appreciating Allah’s greatness, power, and presence. This allows one to belittle the oppressor and not fear him. Barriers to Acquiring the Quality of Backup
Weak faith. Not experiencing or appreciating the brotherhood of faith, leading to not backing up one’s brothers. Examples of Backup from the Life of the Prophets and Companions
❖ This is clear from the story of the man who sought Musa’s support, peace be upon him. Allah, exalted, says: “When he reached full strength and maturity, We gave him wisdom and knowledge. This is how We reward the good-doers. He entered the city unnoticed by its people. There he found two men fighting: one of his own people, and the other of his enemies. The man from his people called to him for help against his foe. So Moses punched him, causing his death. Moses cried, ‘This is from Satan’s handiwork. He is certainly a sworn, misleading enemy.’” al-Qasas: 14 - 15.
❖ The Prophet ﷺ used to exhaust himself in serving others, supporting causes that are for the sake of truth, and backing up the oppressed. He witnessed a treaty in the pre-Islamic era that had been drawn to give the oppressed their right. He ﷺ said in this regard: “I witnessed the treaty of al-Mutayyibin with my uncles as a young boy; it does not please me that now I own red camels, I break it.”  Reported by Ahmad (1655) and al-Bazzar (1000), from the narration of `Abd al-Rahman ibn `Awf, Allah be pleased with him. al-Tabari authenticated it in al-Tafsir (4/1/77). al-Haythami said in Majma` al-Zawa’id (8/175): “Its narrators are those of the authentic.” Tribes from Quraysh came together to agree upon a treaty. They gathered in the house of `Abdullah ibn Jud`an due to his prestige and age. They took covenants that they not find an oppressed person in Makkah - from its natives or otherwise - but they return to him his due rights, and they fend off the oppressor till he returns what is not his. Quraysh called this treaty ‘Hilf al-Fudul’.  Sirat Ibn Hisham (1/133,134).
❖ `Urwa ibn al-Zubayr said: “I asked `Abdullah ibn `Amr ibn al-`As to inform me of the worst thing the pagans had done to Allah’s Messenger ﷺ. He said: ‘While Allah’s Messenger ﷺ was praying in the courtyard of the Ka`bah, `Uqbah ibn Abi Mu`ayt came and seized Allah’s Messenger ﷺ by the shoulder and twisted his garment around his neck and throttled him severely. Abu Bakr came and seized `Uqbah’s shoulder and threw him away from Allah’s Messenger ﷺ and said: “Would you kill a man because he says: ‘My Lord is Allah,’ and has come to you with clear signs from your Lord?!” Ghafir: 28.’”  Reported by al-Bukhari (4815).