when one of you prostrates himself, he should not stretch out his forearms( on the ground) like a dog and he should join both of his thighs.
أَنَّ النَّبِيَّ ﷺ قَالَ إِذَا سَجَدَ أَحَدُكُمْ فَلاَ يَفْتَرِشْ يَدَيْهِ افْتِرَاشَ الْكَلْبِ وَلْيَضُمَّ فَخِذَيْهِ