Camel-Sutrah II (Hadith No. 485)
“The Prophet used to make his she-camel sit across and he would pray facing it (as a Sutra).” I asked, “What would the Prophet do if the she-camel was provoked and moved?” He said, “He would take its camel-saddle and put it in front of him and pray facing its back part (as a Sutra). And Ibn ‘Umar used to do the same.” (This indicates that one should not pray except behind a Sutrah).
Again, one should not pray except behind a sutrah. As to why, you’ll get the answer in the next few days inshaAllah.
Read similar Hadith under Camel-Sutrah.