Skipping the Salat ( Qaza Namaz )
1. Hazrat Anas (ra) had narrated that the Prophet (saws) has said that if a person forgets to recite any salat , he should recite the same afterwards.
( Bukhari ,Muslim )
2. Hazrat Abu Huraira (ra ) had narrated that the prophet ( saws ) has said that if a person slept and misses a particular salat, it will be no sin . But the sin is ,if he skips salat when he is awake . When a person forgets to recite the salat or if skips while sleeping then he should recite the same afterwards.
( Tirmizi, abu Daud )
3. Narrated Mu'adha:
A woman asked 'Aisha, "Should I offer the prayers that which I did not offer because of menses" 'Aisha said, "Are you from the Huraura' (a town in Iraq?) We were with the Prophet and used to get our periods but he never ordered us to offer them (the Prayers missed during menses)." 'Aisha perhaps said, "We did not offer them."
Volume 1, Book 6, Number 318: Sahi Bukhari Sharif