Is it permissible to offer Tahajjud prayer after Witr prayer?

It is permissible to offer voluntary prayer after Witr (An odd number prayer performed between Isha and Fajr) prayer. However, it is desirable that the night prayer be ended with Witr. Therefore, it is desirable for one, who thought that he was most probably going to wake up at night in order to offer Tahajjud, to offer Witr after it, but one, who fears that he might not wake up, should offer Witr before going to bed.

What is the ruling on loudly sending prayers on the Prophet (PBUH ) after the call for prayer Athaan?

All perfect praise be to Allah, The Lord of The Worlds                                                                                                                                                            Sending prayers on the Prophet after Athaan is a Sunnah for the Mou`zen (caller for prayer ) and the hearer. However, there is no harm in doing it loudly after the end of Athaan, but sometimes, it shouldn`t so that people wouldn`t think that it is an integral part of the Athaan. And Allah Knows Best.

Is it permissible for a pious Muslim woman to stay with her husband who had quit praying out of laziness?

Quitting prayer is one of the major grave sins that come after disbelieving in Allah, but the wife of such a person isn`t considered divorced, rather, she should exert all her efforts in order to bring him back to the way of Islam. However, if his sin is likely to lure her from the way of Islam, then she had better separate from him by lawful means such as Mokhal`aa (When a wife pays a compensation for her husband in return for divorcing her). Moreover, if she exercises patience, and remains steadfast on her faith, then there is no harm in doing that.

I have vowed that if Allah gave me what I wanted so bad, I would fast every Monday and Thursday to the rest of my life; unless there is a valid excuse hindering me from doing so. Fortunately, Allah gave me what I wanted, so I started fasting Mondays and Thursdays; however, I stopped out of laziness. What is the Sharia ruling on this?