Accepting a gift or working for someone whose income is haraam

Q: 

1. If all of a person's income is haraam, can you accept a gift of dawat from such a person (i.e. you are sure that he has no halaal wealth or income)? 

2. Can you work for such a person? The work you are doing for him is of a halaal nature, but he is going to pay you your salary from haraam money. 

3. If such a wishes to purchase something from you and you are certain that the money he is paying with haraam money, will it be permissible to sell to him? 

4. Will there be any difference in the ruling if the person (whose income is haraam) is a non-Muslim?

Receiving gifts from a person who works in the bank

Q: I would like advice regarding the following: 

My father works in the bank and it's his only source of income. After finding out that interest is war with Allah Ta'ala, I decided to find a job and move out. 

My question is, now that I have a job and moved out, all the stuff that were bought for me by my father what do I do with it? Do I give it away or can I still use it? My clothing, I have tools my father bought and basically everything I have is from my father, what do I do?

Making a land waqf alal awlaad

Q: 

1. Can a land made waqf alal awlaad be rented out and the recipient(s) of the waqf use the rental money for their personal use? 

2. If my father makes a specific piece of land waqf for me and for my progeny after me and they seize to exist, then it will go to the poor, will the waqf be correct? 

3. After my demise, will the land be in the control of all my children equally (they can all benefit from the land equally or from the rent received from it if it is rented out)? 

4. Similarly, after their demise, will the same apply to all of their children (i.e. my grand children)? 

5. At the time of making waqf, if my father puts a condition that if the mutawalli of the waqf alal awlaad wishes, he/she may sell the waqf land and purchase another land which will be regarded as waqf, will this type of condition be valid.

Repelling the evil whispers of shaitaan in salaaah

Q: Is it permissible/recommended for a person to spit in salaah if he finds whispers of shaitaan troubling him? Is there anything else he should rather do based on authentic narrations? 

The below narration is from Muslim Shareef: 

O Messenger of Allah, the shaytaan interferes between me and my prayer and my recitation, and he makes me confused. The Messenger of Allah (blessings and peace of Allah be upon him) said: “That is a devil called Khinzab. If you feel that, then seek refuge with Allah from him and spit dryly to your left three times.” He said: I did that and Allah took him away from me. 

Please advise.