Is it considered an innovation (bid'ah) to specify the Night Prayer (Qiyam al-Layl) as twelve rak'ahs with the intention of building a house in Paradise, knowing that the prayer of the Prophet (peace and blessings be upon him) was eleven or thirteen rak'ahs? Are the two rak'ahs after every ablution counted as part of Qiyam al-Layl, even if not intended as such? And is it better to stick to only eleven rak'ahs?

It is narrated in Sahih Muslim that the Prophet (peace be upon him) said: "Whoever prays twelve rak'ahs in a day and night, Allah will build for him a house in Paradise thereby." These rak'ahs have been detailed as: four before Dhuhr and two after it, two after Maghrib, two after 'Isha, and two before Fajr. These are the regular supererogatory prayers (Sunan Rawatib), and they are most likely what is intended by the hadith.

The night prayer (Salat al-Layl) is not limited to a specific number, and the best is eleven rak'ahs, following the Sunnah of the Prophet (peace be upon him), but increasing or decreasing them is permissible.