قال شيخ الإسلام ابن تيمية :
فأمَّا قوله صلى الله عليه وسلم ” أما الركوع فعظِّموا فيه الربَّ ، وأمَّا السجود فاجتهدوا في الدعاء فَقَمِنٌ ( أي : حقيق وجدير ) أنْ يستجاب لكم ” – رواه مسلم . ففيه الأمر في الركوع بالتعظيم ، وأمره بالدعاء في السجود بيانٌ منه أنَّ الدعاء في السجود أحق بالإجابة من الركوع
، ولهذا قال : ” فقمِنٌ أنْ يُستجاب لكم “ كما قال : ” أقرب ما يكون العبد من ربِّه وهو ساجدٌ “ – رواه مسلم – فهو أمرٌ بأنْ يكون الدعاء في السجود .
” مجموع الفتاوى “
Regarding the words of the Prophet (peace and blessings of Allah be upon him),
“As for rukoo’, glorify your Lord there, and as for sujood (prostration) strive in du’aa’ therein, because then it is more likely that you will be answered” (narrated by Muslim) – this has the command to glorify Allah in rukoo’, and the command to make du’aa’ when prostrating indicates that du’aa’ in sujood is more likely to be answered than in rukoo’.
Hence he said, “because then it is more likely that you will be answered”. Likewise he also said, “The closest that the slave is to his Lord is when he is prostrating.” (Narrated by Muslim). This is a command that du’aa’ should be made in sujood.
Majmu’ al-Fatawa, 22/378

bismillaahir rahmaanir raheem
assalaamu’alaikum
how do you interpret the use of the term ‘command’?
wa 3alaykum al salam wa rahmatullahi wa barakatuh;
The command here is not a order of obligation; the second part explains the command i.e that the supplication is more likely to be accepted in such a position.