What is the ruling on touching old books that bear the names of Allah Almighty, and may be dirty, and is it obligatory to ensure their purity before touching them?

Books containing the names of Allah, or His remembrance, or His verses, must be placed in suitable locations, far from anything that would expose them to harm or defilement. This is a sign of piety in the hearts, as Allah the Almighty says: (That [is so]. And whoever honors the symbols of Allah – indeed, it is from the piety of hearts.) and (That [is so]. And whoever honors the sacred ordinances of Allah – it is better for him in the sight of his Lord.). If they are touched by any defilement, it must be removed. Nothing is ruled ritually impure merely by doubt.