After the detention of young Benyamin in Egypt, his brothers returned home and told Sayyidna Ya` qub (علیہ السلام) about what had happened there. They tried to assure him that they were telling the truth which can be confirmed from the people in Egypt, as well as, from the caravan they came with from Egypt to Canaan. From the later, he could also ascertain that Benyamin's theft was apprehended and he was arrested for it. Since Sayyidna Ya` qub (علیہ السلام) knew that they had lied to him earlier in the case of Sayyidna Yusuf (علیہ السلام) ، therefore, he could not believe them this time too - though, in fact, this time they had told him no lie. And therefore, on this occasion as well, he said the same thing he had said at the time of the disappearance of Sayyidna Yusuf (علیہ السلام) : بَلْ سَوَّلَتْ لَكُمْ أَنفُسُكُمْ أَمْرًا ۖ فَصَبْرٌ جَمِيلٌ. ("Rather, your inner desires have seduced you to something. So, patience is best), that is, this statement of yours is not correct. You have made it up yourself. But, even now, it is patience I choose to observe. Only that would be the best for me.'
From this Al-Qurtubi has deduced: In whatever a Mujtahid says with his Ijtihad, there can be an error as well, so much so that it is possible that a prophet too, when he says something on the basis of his own Ijtihad, could make an error - though, only initially. This is what happened in this case when he declared the truth of his sons to be a lie. But, prophets have a special status and a personal exclusivity on the basis of which they are alerted over the mistake by the will of Allah, and removed away from it, and finally they find truth.
Here, it is also possible that by his comment about 'maneuvering something' mentioned above Sayyidna Ya` qub (علیہ السلام) intended to refer to what was made up in Egypt whereby Benyamin was arrested under a false charge of theft only to achieve a particular purpose, and the ultimate result of which was to unfold later in a better form. There may, as well, be a hint toward it in the next sentence of this verse where it is said: عَسَى اللَّـهُ أَن يَأْتِيَنِي بِهِمْ جَمِيعًا (Hopefully, Allah may bring them all together).
In short, the outcome of the refusal of Sayyidna Ya` qub (علیہ السلام) to accept the statement of his sons this time was that there was no theft really, nor was Benyamin arrested, and the truth of the matter was to be found elsewhere. This was true in its place. But, whatever was said by his sons, as they knew it, was not wrong either.