Surah 12. Yusuf, Ayah 13

Jacob did not know the precise plot, but he had strong misgivings. But how could he put off these brethren? If they were driven to open hostility, they would be certain to cause him harm. He must deal with the brethren wisely and cautiously. He pleaded that he was an old man, and would miss Joseph and be sad without him. And after all, Joseph was not of an age to play with them. They would be attending to their own affairs, and a wolf might come and attack and kill Joseph. In saying this he was really unwittingly giving a cue to the wicked ones, for they use that very excuse in verse 17 below. Thus the wicked plot thickens, but there is a counter-plan also, which is drawing a noose of lies round the wicked ones, so that they are eventually driven into a corner, and have to confess their own guilt in verse 91 below, and through repentance obtain forgiveness.