وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ يَحْيَى بْنِ سَعِيدٍ، قَالَ رَأَيْتُ أَنَسَ بْنَ مَالِكٍ فِي السَّفَرِ وَهُوَ يُصَلِّي عَلَى حِمَارٍ وَهُوَ مُتَوَجِّهٌ إِلَى غَيْرِ الْقِبْلَةِ يَرْكَعُ وَيَسْجُدُ إِيمَاءً مِنْ غَيْرِ أَنْ يَضَعَ وَجْهَهُ عَلَى شَىْءٍ ‏.‏

Yahya related to me from Malik that Yahya ibn Said said, "I sawAnas ibn Malik on a journey praying on a donkey facing away from theqibla. He did the raka and the sajda by motioning with his head,without putting his face on anything." Translation Not Available

Book Ref: Muwatta Imam Malik Book 9 Hadith 358
Web Ref:  Muwatta Imam Malik Book 9 Hadith 29