All perfect praise be to Allah the Lord of The Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
Ruling of Sharia on working in a conventional bank varies according to situation:
1- If the employee doesn`t directly deal with usury transactions and doesn`t facilitate for that then he isn`t sinful.
2- If the employee directly deals in usury transactions and facilitates for that, then this isn`t permissible because Allah the Almighty says, {What means} " Help ye one another in righteousness and piety, but help ye not one another in sin and rancour: fear Allah. for Allah is strict in punishment." {Al-Mai`da, 2}. Moreover, Allah's Messenger (PBUH) cursed the one who accepts usury, the one who gives it, the one who records it and the two witnesses to it, saying: "They are all the same." [Reported by Muslim]. Commenting on this Hadith, An-Nawawi said: "It prohibits helping in sin." {Shareh Muslim,vol.11/pp.26}.
Saving money from an unlawful job until finding a lawful one is totally unacceptable because Allah doesn`t bless ill-gotten money and your intention doesn`t make the unlawful work lawful. You (Asker) should ponder upon the above narration and choose which party you would like to be gathered with on the Day of Judgement.
We (Iftaa` Dept.) remind you that Allah Says (What means): "Thus when they fulfil their term appointed, either take them back on equitable terms or part with them on equitable terms; and take for witness two persons from among you, endued with justice, and establish the evidence (as) before God. Such is the admonition given to him who believes in God and the Last Day. And for those who fear God, He (ever) prepares a way out, And He provides for him from (sources) he never could imagine. And if any one puts his trust in God, sufficient is (God) for him. For God will surely accomplish his purpose: verily, for all things has God appointed a due proportion." {At-Talaq, 2-3}. And Allah The Almighty Knows Best.