Abu Muslim says that once I asked Hazrat Abu Dharr (may Allah be pleased with him), "Which part of the night is the best for standing (in prayer)?" He replied, "The way you have asked me this question, I also asked the Noble Prophet (peace and blessings be upon him), and the Noble Prophet (peace and blessings be upon him) said, 'In the last half of the night.' But those who do so are very few."
Hadith Referenceمسند احمد / مسند الأنصار رضي الله عنهم / 21555
Hadith Gradingحکم دارالسلام:صحيح لغيره، وهذا إسناد ضعيف، المهاجر أبو خالد فيه لين، وأبو مسلم مجهول