Ibn Baz: Permissible and Impermissible Fears  

Shaikh Ibn Bāz, may Allāh have mercy on him, said:

There is no sin on a Muslim [for] his fearing things that are naturally harmful like predatory animals, snakes, and the like, so that he then takes means to guard himself using protective measures, just as there is no sin on Muslims in their having a fear of their enemy to the point they prepare [militarily], preparations that have been legislated in Islāmic legislation as Allāh, All-Perfect is He, says:

Make preparations for them with whatever you are able [to amass] of might. [English meaning, from Al-Anfāl: 60]

Which means:  [make preparations for] the enemies, while relying on Allāh, placing full faith in Him, and believing that victory is from Him.

And a believer only takes measures and makes [whatever] preparations [are called for] because Allāh, All-Perfect is He, has commanded him with them, not due to his relying on them, as Allāh, All-Perfect is He, says:

When you pleaded for your Lord’s help at a time of dire need, and then He responded to you that I will certainly send you reinforcements of a thousand angels coming one after another in succession.

And Allāh did not make that [reinforcement of  angels] other than a glad tiding for you [of His granting you victory over your enemies] and so your hearts would find rest and surety [in knowing of the coming victory He would grant you], and there is no victory except from Allāh; indeed, Allāh is Almighty, All-Wise. [English meaning of Al-Anfāl: 9-10]

The only type of fear Allāh has prohibited is fear of creation in a way that leads to the one having [such fear] leaving an obligatory action [in Islām] or committing a sin; in that regard His [following] speech, All-Perfect is He, was revealed:

So do not fear them but fear Me if you are believers. [English meaning, from Āli ‘Imrān: 175]

And the like of that [in being forbidden] is fearing other than Allāh by way of worship, and believing that he [the one wrongly such feared] knows the Unseen, has control in managing the affairs of all existence, or can cause harm or benefit without Allāh’s willing [that], as the Mushrikūn [those who worship others along with Allāh] do with the ones they worship.

And from Allāh is all [true] success.

Source: http://www.binbaz.org.sa/fatawa/303