عَنِ ابْنِ عَبَّاسٍ رَضِيَ اللَّهُ عَنْهُ قَالَ: سَأَلَ رَجُلٌ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ عَنْ شَيْءٍ مِنْ أَمْرِ الصَّلَاةِ فَقَالَ لَهُ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ: خَلِّلْ أَصَابِعَ يَدَيْكَ وَرِجْلَيْكَ يَعْنِي إِسْبَاغَ الْوُضُوءِ، وَكَانَ فِيمَا قَالَ لَهُ: إِذَا رَكَعْتَ فَضَعْ كَفَّيْكَ عَلَى رُكْبَتَيْكَ حَتَّى تَطْمَئِنَّ (وَفِي رِوَايَةٍ: حَتَّى تَطْمَئِنَّا) وَإِذَا سَجَدْتَ فَأَمْكِنْ جَبْهَتَكَ مِنَ الْأَرْضِ حَتَّى تَجِدَ حَجْمَ الْأَرْضِ
Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) says: A man asked the Noble Prophet (peace and blessings be upon him) about prayer. The Messenger of Allah (peace and blessings be upon him) said: "Cleanse between the fingers of the hands and feet." By this, he meant that ablution should be performed completely. Furthermore, the Prophet (peace and blessings be upon him) also said to him: "When you bow (in ruku‘), place your palms on your knees and be at ease in the position of ruku‘, and when you prostrate (in sujud), place your forehead firmly on the ground, until you feel the thickness of the earth."