It is narrated from Hazrat Aisha (may Allah be pleased with her) that the Prophet (peace and blessings be upon him) said: The reward for offering prayer while sitting is half of the reward for offering prayer while standing.
Hadith Referenceمسند احمد / مسند النساء / 24426
Hadith Gradingحکم دارالسلام:حديث صحيح لغيره دون قوله غير متربع فزيادة منكرة تفرد بها شريك