Is Qiyaam al-Layl an excuse not to have intimate relations with the husband?

Question 51: Is it permissible for a wife to refuse to be in bed with her husband under the excuse that she observes Qiyaam al-Layl (optional Prayer at night) or says Tasbeeh (saying: “Subhaan Allaah [Glory be to Allaah]”)? Are such things Shar`ee (Islaamically lawful) excuses for her?

Answer: No, they are not Shar`ee excuses for her; as fulfilling the husband’s rights is obligatory while observing Qiyaam-ul-Layl and Tasbeeh are acts of Sunnah (supererogatory acts of worship following the example of the Prophet). The obligatory act of worship prevails over the acts of Sunnah. On the authority of Aboo Hurayrah (may Allaah be pleased with him) who narrated that Allaah’s Messenger (peace be upon him) said... read more here.

Is there a specific number of Rak`ahs for optional Qiyaam al-Layl

Question 17:  Is it necessary to offer a specific number of Rak`ahs (units of Prayer) for Qiyaam-ul-Layl (standing for optional Prayer at night) every night or is it done according to one’s ability?

Answer: It is prescribed for a Muslim to offer eleven Rak`ahs on standing for optional night Salaah (Prayer), as this was the number mostly observed by the Prophet (peace be upon him). It was authentically reported that `Aa’ishah (may Allaah be pleased with her) said... read more here.