What is the reason that the reward for one who goes out for the Forenoon Glorification (tasbih al-Duha) in the hadith is limited to the reward of only the performer of 'Umrah, even though it is well-known that he receives the reward of a complete Hajj and 'Umrah? And what is the meaning of "لا ينصبه إلا إياه" (nothing causes him to undertake it except it)?

The hadith is authentic, graded as good by Al-Albani, and it is understood from it that the reward for a complete Hajj and Umrah is attained by whoever remains in the place where he prayed Fajr in congregation, remembering Allah until the sun rises, and then prays two rak'ahs. As for someone who goes to his work or home and then leaves to pray Duha, he only receives the reward of an 'Umrah performer. There is no contradiction between the two hadiths, and the meaning of "nothing wearies him but it" means that only that effort tires him. The intent is the effort and exertion a Muslim expends in leaving worldly occupations to perform the Duha prayer.