Get Android ICS stock firmware for Lenovo A789 Smartphone from here or from here. Get previous firmware from here.
Firmware details
Archive: Lenovo_A789 4.0.4 fw
Image: Lenovo_A789_VIBE_SJDS_20150316/Lenovo_A789_VIBE_SJJL_20150316
Archive: Lenovo_A789 4.0.4 fw
Image: Lenovo_A789_VIBE_SJDS_20150316/Lenovo_A789_VIBE_SJJL_20150316
Model: Lenovo A789 Smartphone
Image file size: 406 MB
Platform: Mediatek MT6577
Build number: A789-user 4.0.4 IMM76D A789_S235_130828 release-keys
Caution: Please do not update firmware unless you know what you are doing, you really want it or it is absolutely necessary. Firmware updates may occasionally have bad results, like bricking your device, temporarily or permanently. The firmware update process is done entirely at your own risk. Before attempting to update the firmware, back up your data.
Build number: A789-user 4.0.4 IMM76D A789_S235_130828 release-keys
Caution: Please do not update firmware unless you know what you are doing, you really want it or it is absolutely necessary. Firmware updates may occasionally have bad results, like bricking your device, temporarily or permanently. The firmware update process is done entirely at your own risk. Before attempting to update the firmware, back up your data.