Credit cards

Q: I have a question about credit card's if you could please answer it, My question is this: Are credit card's Halaal?

To elaborate on this - if a company offers me 10,000 euros to spend on a card as and when I wish and all I have to do is pay back what I have used in 30 days and no charges will be applied to my month bill, BUT if I don't pay off this amount that I have used in the past 30 days then they will add interest to my repayments, like 15% of what I have used every month till I pay it off and based on this I agree and I enter into this agreement with that company and take and use this card. My intention is to pay off my bill every month before any interest is applied so I don't pay any Riba (interest) and I do, I keep up with my repayments every time and I don't not pay any interest at any point. But I have agreed that if I do miss a payment that I will pay them the interest. Is this permissible? Is it allowed for a Muslim to enter such a contract to make a agreement to pay Riba(interest) if such and such happens, but the Muslims intention is to never be in that situation but yet still agreeing that if I do fall in that situation I will pay you with interest. A brother of mine fell on hard times and he took a credit card to get himself through this hard times and he told me that some Ulema have said that it is permissible if you need it and as long as you stay within the monthly repayments without the add of interest. My understanding is that a Muslim must live by his oath and even agreeing to do Haram(whether or not you do it) is Haraam.

Jazak'Allah Khayrr for your time and I wait to hear your reply and clarity on this matter.

Performing nafl salaah with the intention of qadha for any salaah one may have missed

Q: Is it possible to make intention during nafl salaah that the nafl salaah be accepted for any qadha salaahs that one may have - specifically qadha salaahs that one may not be knowing of e.g. when ghusl after menstruation has been delayed or when a salaah may not have been performed in a state of wudhu unintentionally or one's ankles/hair may have been exposed, thus rendering salaah invalid?