It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that he (peace and blessings be upon him) said: "Is any one of you unable, after offering the obligatory prayer, to move a little forward or back, or to the right or left, from that place in order to offer voluntary prayer?"
Imam al-Bukhari (may Allah have mercy on him) said: Isma'il bin Ibrahim is more correct, and Layth is inconsistent (mudtarib) in it. He is Layth bin Abi Sulaym, and he alone narrated it. And Allah Almighty knows best.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3045