All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.
The hadeeth that you mentioned is an authentic hadeeth that was narrated by Muslim, Ahmad and others. It clarifies that it is permissible to seek cure from the clothes worn by the Prophet because of the blessings that they have. This corresponds to other authentic ahaadeeth regarding seeking blessings with the effects of the Prophet such as his sweat and his hair. For more benefit, please refer to fataawa 25217 and 88236.
However, this is a way of seeking blessings and not a way of seeking intercession. The scholars do not have any difference of opinion on the permissibility of seeking this blessing, but this is peculiar to the Prophet as his Companions did not seek blessings with the effects of any other person than him .
The Fiqh Encyclopedia reads:
“The scholars agreed on the permissibility of seeking blessings with the Prophet and his relics, and the scholars of biography, virtues and Hadeeth reported a lot of information that shows that the Companions sought blessings in various forms from the Prophet and his relics. Ibn Rajab said: 'Seeking blessings with the relics (of the Prophet ) is something that the Companions used to do with the Prophet but they did not do so with each other, and the Taabi’is (the generation that followed that of the Companions) did not do so with the Companions despite the great status of the latter. This is evidence that this cannot be done except with the Prophet such as seeking blessings in the water that he used to perform wudhoo' (ablution) with, and with his other relics.”
However, this hadeeth has nothing to do with the Unseen; rather, Allaah informed the Prophet about many matters of the unseen, and the Prophet informed us about them, some of them have happened and some have not yet taken place. For more benefit, please refer to fatwa only knew the unseen that Allaah informed him about">91400.
Allaah knows best.