In a lengthy narration, Imam Sadiq (عليه السلام) says,

إِنَّ عَلَى الْكَوْثَرِ أَمِيرَ الْمُؤْمِنِينَ (ع) وَ فِي يَدِهِ عَصًا مِنْ عَوْسَجٍ يَحْطِمُ بِهَا أَعْدَاءَنَا فَيَقُولُ الرَّجُلُ مِنْهُمْ إِنِّي أَشْهَدُ الشَّهَادَتَيْنِ فَيَقُولُ انْطَلِقْ إِلَى إِمَامِكَ فُلَانٍ- فَاسْأَلْهُ أَنْ يَشْفَعَ لَكَ فَيَقُولُ تَبَرَّأَ مِنِّي إِمَامِيَ الَّذِي تَذْكُرُهُ فَيَقُولُ ارْجِعْ إِلَى وَرَائِكَ فَقُلْ لِلَّذِي كُنْتَ تَتَوَلَّاهُ وَ تُقَدِّمُهُ عَلَى الْخَلْقِ فَاسْأَلْهُ إِذَا كَانَ خَيْرَ الْخَلْقِ عِنْدَكَ أَنْ يَشْفَعَ لَكَ- فَإِنَّ خَيْرَ الْخَلْقِ مَنْ يَشْفَعُ [حَقِيقٌ أَنْ لَا يُرَدَّ إِذَا شَفَعَ] فَيَقُولُ إِنِّي أَهْلِكُ عَطَشاً فَيَقُولُ لَهُ زَادَكَ اللَّهُ ظَمَأً وَ زَادَكَ اللَّهُ عَطَشاً قُلْتُ جُعِلْتُ فِدَاكَ وَ كَيْفَ يَقْدِرُ عَلَى الدُّنُوِّ مِنَ الْحَوْضِ وَ لَمْ يَقْدِرْ عَلَيْهِ غَيْرُهُ فَقَالَ وَرِعَ عَنْ أَشْيَاءَ قَبِيحَةٍ وَ كَفَّ عَنْ شَتْمِنَا أَهْلَ الْبَيْتِ إِذَا ذُكِرْنَا وَ تَرَكَ أَشْيَاءَ اجْتَرَى عَلَيْهَا غَيْرُهُ وَ لَيْسَ ذَلِكَ لِحُبِّنَا وَ لَا لِهَوًى مِنْهُ لَنَا وَ لَكِنَّ ذَلِكَ لِشِدَّةِ اجْتِهَادِهِ فِي عِبَادَتِهِ وَ تَدَيُّنِهِ وَ لِمَا قَدْ شَغَلَ نَفْسَهُ بِهِ عَنْ ذِكْرِ النَّاسِ فَأَمَّا قَلْبُهُ فَمُنَافِقٌ وَ دِينُهُ النَّصْبُ وَ اتِّبَاعُهُ أَهْلَ النَّصْبِ وَ وَلَايَةُ الْمَاضِينَ وَ تَقَدُّمُهُ تَقْدِيمُهُ لَهُمَا عَلَى كُلِّ أَحَدٍ

Amir al-Momineen (عليه السلام) will be standing by Hauz Kauthar with a thorny stick, with which he will beat Our enemies in such a way that one of them will say, "I bear witness of the 2 testimonies (i.e. That there is no god but Allah and Muhammad (ص) is Allah’s Messenger)."

Imam (عليه السلام) will reply, "Go to your so and so leader (Imam) and ask him to intercede for you."

The man will say, "My leader, whom you mentioned, dissociates himself from me."

Amirul al-Momineen (عليه السلام) will reply, "Go back and ask the one whom you used to love, follow and whom you preferred above the rest of creation to intercede for you, since he was the best of creation in your eyes, for indeed only the best of creation can intercede."

The man will say, "I am dying of thirst!"

Amirul Momineen (عليه السلام) will reply, "May Allah aggravate your thirst and need for water!"

I (the narrator) asked Imam Sadiq (عليه السلام), "May I be sacrificed on you, how can he even come near the Pool when others cannot?"

Imam Sadiq (عليه السلام) replied, "He stayed away from evil acts and abstained from insulting us when we were mentioned in his presence and he avoided some other sinful acts that others dared to commit. But this was not based on following Us or loving Us. On the contrary, it was based on his intense efforts in worship and religious acts and on being preoccupied with himself rather than talking about others. But his heart was filled with hypocrisy and his religion was based upon hating us, following those who had hatred towards Us, believing in the authority of those two persons of the past and giving preference to them over everyone else."

(only required portion of the hadith quoted here)

[Source: Kamil al-Ziyarat, Chapter. 32, Hadith. 6]