It is narrated from Sayyiduna Thawban (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When one of you has prayed witr, let him pray two rak'ahs (after it). Then if he is able to get up (again at night for prayer, that is better); otherwise those two rak'ahs will count for him (in place of tahajjud)."
Imam al-Tabarani (may Allah have mercy on him) said: "This hadith is not narrated from Sayyiduna Thawban (may Allah be pleased with him) except with this chain, and Ibn Wahb (may Allah have mercy on him) is alone in narrating it."
Hadith Referenceالمعجم الأوسط / باب الميم / 6439
Hadith Takhrij«أخرجه ابن خزيمة فى «صحيحه» برقم: 1106، وابن حبان فى «صحيحه» برقم: 2577، والدارمي فى «مسنده» برقم: 1635، والبيهقي فى «السنن الكبرى» برقم: 4902، والدارقطني فى «سننه» برقم: 1683، 1681، والبزار فى «مسنده» برقم: 4193، والطحاوي فى «شرح معاني الآثار» برقم: 2011، والطبراني فى «الكبير» برقم: 1410»